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 $80.73   8.464%   $87.563   $87.56   $87.55   $87.60  
  Purchase #2 $236.90   8.363%   $256.7119   $256.71   $256.70   $256.70  
  Purchase #3 $86.79   10.680%   $96.0592   $96.06   $96.05   $96.10  
  Purchase #4 $235.85   6.635%   $251.4986   $251.50   $251.50   $251.50  
  Purchase #5 $23.51   10.618%   $26.0063   $26.01   $26.00   $26.00  
  Purchase #6 $87.31   5.237%   $91.8824   $91.88   $91.90   $91.90  
  Purchase #7 $86.30   11.664%   $96.366   $96.37   $96.35   $96.40  
  7 purchase totals = $837.39       $906.0874   $906.09   $906.05   $906.20