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 $71.33   6.458%   $75.9365   $75.94   $75.95   $75.90  
  Purchase #2 $138.61   10.196%   $152.7427   $152.74   $152.75   $152.70  
  Purchase #3 $205.37   11.718%   $229.4353   $229.44   $229.45   $229.40  
  Purchase #4 $106.57   7.835%   $114.9198   $114.92   $114.90   $114.90  
  Purchase #5 $114.65   13.754%   $130.419   $130.42   $130.40   $130.40  
  Purchase #6 $179.89   10.714%   $199.1634   $199.16   $199.15   $199.20  
  Purchase #7 $50.84   6.772%   $54.2829   $54.28   $54.30   $54.30  
  7 purchase totals = $867.26       $956.8996   $956.90   $956.90   $956.80