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 $68.33   6.864%   $73.0202   $73.02   $73.00   $73.00  
  Purchase #2 $238.37   7.433%   $256.088   $256.09   $256.10   $256.10  
  Purchase #3 $58.79   5.457%   $61.9982   $62.00   $62.00   $62.00  
  Purchase #4 $136.62   3.154%   $140.929   $140.93   $140.95   $140.90  
  Purchase #5 $70.85   9.405%   $77.5134   $77.51   $77.50   $77.50  
  Purchase #6 $78.30   8.242%   $84.7535   $84.75   $84.75   $84.80  
  Purchase #7 $103.35   13.137%   $116.9271   $116.93   $116.95   $116.90  
  7 purchase totals = $754.61       $811.2294   $811.23   $811.25   $811.20