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 $65.95   4.111%   $68.6612   $68.66   $68.65   $68.70  
  Purchase #2 $76.52   12.355%   $85.974   $85.97   $85.95   $86.00  
  Purchase #3 $201.46   10.609%   $222.8329   $222.83   $222.85   $222.80  
  Purchase #4 $166.93   13.502%   $189.4689   $189.47   $189.45   $189.50  
  Purchase #5 $145.30   12.522%   $163.4945   $163.49   $163.50   $163.50  
  Purchase #6 $13.47   7.369%   $14.4626   $14.46   $14.45   $14.50  
  Purchase #7 $201.66   11.444%   $224.738   $224.74   $224.75   $224.70  
  7 purchase totals = $871.29       $969.6321   $969.62   $969.60   $969.70