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 $46.57   6.142%   $49.4303   $49.43   $49.45   $49.40  
  Purchase #2 $101.97   10.530%   $112.7074   $112.71   $112.70   $112.70  
  Purchase #3 $154.40   9.449%   $168.9893   $168.99   $169.00   $169.00  
  Purchase #4 $232.28   11.581%   $259.1803   $259.18   $259.20   $259.20  
  Purchase #5 $167.88   3.220%   $173.2857   $173.29   $173.30   $173.30  
  Purchase #6 $74.89   3.583%   $77.5733   $77.57   $77.55   $77.60  
  Purchase #7 $188.80   8.687%   $205.2011   $205.20   $205.20   $205.20  
  7 purchase totals = $966.79       $1,046.3674   $1,046.37   $1,046.40   $1,046.40