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 $34.89   4.649%   $36.512   $36.51   $36.50   $36.50  
  Purchase #2 $72.98   4.191%   $76.0386   $76.04   $76.05   $76.00  
  Purchase #3 $205.92   10.262%   $227.0515   $227.05   $227.05   $227.10  
  Purchase #4 $226.98   8.762%   $246.868   $246.87   $246.85   $246.90  
  Purchase #5 $24.49   11.302%   $27.2579   $27.26   $27.25   $27.30  
  Purchase #6 $87.29   4.416%   $91.1447   $91.14   $91.15   $91.10  
  Purchase #7 $241.46   10.560%   $266.9582   $266.96   $266.95   $267.00  
  7 purchase totals = $894.01       $971.8309   $971.83   $971.80   $971.90