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 $88.65   4.856%   $92.9548   $92.95   $92.95   $93.00  
  Purchase #2 $143.25   8.445%   $155.3475   $155.35   $155.35   $155.30  
  Purchase #3 $187.67   7.837%   $202.3777   $202.38   $202.40   $202.40  
  Purchase #4 $22.30   12.476%   $25.0821   $25.08   $25.10   $25.10  
  Purchase #5 $125.79   3.624%   $130.3486   $130.35   $130.35   $130.30  
  Purchase #6 $86.28   13.276%   $97.7345   $97.73   $97.75   $97.70  
  Purchase #7 $53.46   12.597%   $60.1944   $60.19   $60.20   $60.20  
  7 purchase totals = $707.40       $764.0396   $764.03   $764.10   $764.00