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 $42.97   12.145%   $48.1887   $48.19   $48.20   $48.20  
  Purchase #2 $68.87   6.717%   $73.496   $73.50   $73.50   $73.50  
  Purchase #3 $155.47   5.840%   $164.5494   $164.55   $164.55   $164.50  
  Purchase #4 $102.92   3.391%   $106.41   $106.41   $106.40   $106.40  
  Purchase #5 $172.49   8.625%   $187.3673   $187.37   $187.35   $187.40  
  Purchase #6 $8.79   12.708%   $9.907   $9.91   $9.90   $9.90  
  Purchase #7 $221.64   6.615%   $236.3015   $236.30   $236.30   $236.30  
  7 purchase totals = $773.15       $826.2199   $826.23   $826.20   $826.20