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 $149.62   3.445%   $154.7744   $154.77   $154.75   $154.80  
  Purchase #2 $186.38   7.615%   $200.5728   $200.57   $200.55   $200.60  
  Purchase #3 $19.66   11.523%   $21.9254   $21.93   $21.95   $21.90  
  Purchase #4 $65.83   13.560%   $74.7565   $74.76   $74.75   $74.80  
  Purchase #5 $213.28   5.263%   $224.5049   $224.50   $224.50   $224.50  
  Purchase #6 $152.53   10.733%   $168.901   $168.90   $168.90   $168.90  
  Purchase #7 $155.90   8.583%   $169.2809   $169.28   $169.30   $169.30  
  7 purchase totals = $943.20       $1,014.7159   $1,014.71   $1,014.70   $1,014.80