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 $78.53   11.697%   $87.7157   $87.72   $87.70   $87.70  
  Purchase #2 $23.75   5.220%   $24.9898   $24.99   $25.00   $25.00  
  Purchase #3 $110.85   10.601%   $122.6012   $122.60   $122.60   $122.60  
  Purchase #4 $77.94   10.868%   $86.4105   $86.41   $86.40   $86.40  
  Purchase #5 $58.58   7.333%   $62.8757   $62.88   $62.90   $62.90  
  Purchase #6 $225.83   8.615%   $245.2853   $245.29   $245.30   $245.30  
  Purchase #7 $126.66   5.399%   $133.4984   $133.50   $133.50   $133.50  
  7 purchase totals = $702.14       $763.3766   $763.39   $763.40   $763.40