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 $24.45   9.372%   $26.7415   $26.74   $26.75   $26.70  
  Purchase #2 $114.85   4.344%   $119.8391   $119.84   $119.85   $119.80  
  Purchase #3 $150.86   7.498%   $162.1715   $162.17   $162.15   $162.20  
  Purchase #4 $235.89   12.506%   $265.3904   $265.39   $265.40   $265.40  
  Purchase #5 $225.52   11.591%   $251.66   $251.66   $251.65   $251.70  
  Purchase #6 $249.80   5.603%   $263.7963   $263.80   $263.80   $263.80  
  Purchase #7 $188.92   5.813%   $199.9019   $199.90   $199.90   $199.90  
  7 purchase totals = $1,190.29       $1,289.5007   $1,289.50   $1,289.50   $1,289.50