Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $117.87   12.433%   $132.5248   $132.52   $132.50   $132.50  
  Purchase #2 $248.62   8.471%   $269.6806   $269.68   $269.70   $269.70  
  Purchase #3 $150.34   7.681%   $161.8876   $161.89   $161.90   $161.90  
  Purchase #4 $122.83   11.139%   $136.512   $136.51   $136.50   $136.50  
  Purchase #5 $142.42   12.586%   $160.345   $160.35   $160.35   $160.30  
  Purchase #6 $107.87   10.399%   $119.0874   $119.09   $119.10   $119.10  
  Purchase #7 $230.74   6.113%   $244.8451   $244.85   $244.85   $244.80  
  7 purchase totals = $1,120.69       $1,224.8825   $1,224.89   $1,224.90   $1,224.80