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 $41.92   10.797%   $46.4461   $46.45   $46.45   $46.40  
  Purchase #2 $158.82   12.236%   $178.2532   $178.25   $178.25   $178.30  
  Purchase #3 $188.99   4.352%   $197.2148   $197.21   $197.20   $197.20  
  Purchase #4 $88.47   4.722%   $92.6476   $92.65   $92.65   $92.60  
  Purchase #5 $216.61   9.857%   $237.9612   $237.96   $237.95   $238.00  
  Purchase #6 $59.84   12.835%   $67.5205   $67.52   $67.50   $67.50  
  Purchase #7 $13.79   8.467%   $14.9576   $14.96   $14.95   $15.00  
  7 purchase totals = $768.44       $835.0010   $835.00   $834.95   $835.00