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 $66.83   11.802%   $74.7173   $74.72   $74.70   $74.70  
  Purchase #2 $235.96   12.612%   $265.7193   $265.72   $265.70   $265.70  
  Purchase #3 $228.99   3.790%   $237.6687   $237.67   $237.65   $237.70  
  Purchase #4 $20.63   11.579%   $23.0187   $23.02   $23.00   $23.00  
  Purchase #5 $5.57   6.790%   $5.9482   $5.95   $5.95   $5.90  
  Purchase #6 $211.36   9.130%   $230.6572   $230.66   $230.65   $230.70  
  Purchase #7 $61.32   6.709%   $65.434   $65.43   $65.45   $65.40  
  7 purchase totals = $830.66       $903.1634   $903.17   $903.10   $903.10