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 $107.95   10.791%   $119.5989   $119.60   $119.60   $119.60  
  Purchase #2 $146.71   13.801%   $166.9574   $166.96   $166.95   $167.00  
  Purchase #3 $51.73   7.687%   $55.7065   $55.71   $55.70   $55.70  
  Purchase #4 $191.52   3.687%   $198.5813   $198.58   $198.60   $198.60  
  Purchase #5 $61.52   12.648%   $69.301   $69.30   $69.30   $69.30  
  Purchase #6 $142.87   3.511%   $147.8862   $147.89   $147.90   $147.90  
  Purchase #7 $15.81   9.371%   $17.2916   $17.29   $17.30   $17.30  
  7 purchase totals = $718.11       $775.3229   $775.33   $775.35   $775.40