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 $78.95   11.471%   $88.0064   $88.01   $88.00   $88.00  
  Purchase #2 $23.69   10.867%   $26.2644   $26.26   $26.25   $26.30  
  Purchase #3 $238.75   10.780%   $264.4873   $264.49   $264.50   $264.50  
  Purchase #4 $63.26   12.427%   $71.1213   $71.12   $71.10   $71.10  
  Purchase #5 $30.88   8.827%   $33.6058   $33.61   $33.60   $33.60  
  Purchase #6 $158.45   10.191%   $174.5976   $174.60   $174.60   $174.60  
  Purchase #7 $65.52   4.219%   $68.2843   $68.28   $68.30   $68.30  
  7 purchase totals = $659.50       $726.3671   $726.37   $726.35   $726.40