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 $187.91   4.855%   $197.033   $197.03   $197.05   $197.00  
  Purchase #2 $59.35   10.460%   $65.558   $65.56   $65.55   $65.60  
  Purchase #3 $140.44   9.483%   $153.7579   $153.76   $153.75   $153.80  
  Purchase #4 $48.27   12.573%   $54.339   $54.34   $54.35   $54.30  
  Purchase #5 $36.34   9.826%   $39.9108   $39.91   $39.90   $39.90  
  Purchase #6 $29.42   6.688%   $31.3876   $31.39   $31.40   $31.40  
  Purchase #7 $215.46   11.340%   $239.8932   $239.89   $239.90   $239.90  
  7 purchase totals = $717.19       $781.8795   $781.88   $781.90   $781.90