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 $66.98   13.262%   $75.8629   $75.86   $75.85   $75.90  
  Purchase #2 $218.30   7.177%   $233.9674   $233.97   $233.95   $234.00  
  Purchase #3 $129.35   3.197%   $133.4853   $133.49   $133.50   $133.50  
  Purchase #4 $215.75   12.134%   $241.9291   $241.93   $241.95   $241.90  
  Purchase #5 $75.33   12.536%   $84.7734   $84.77   $84.75   $84.80  
  Purchase #6 $6.32   9.229%   $6.9033   $6.90   $6.90   $6.90  
  Purchase #7 $203.26   3.799%   $210.9818   $210.98   $211.00   $211.00  
  7 purchase totals = $915.29       $987.9032   $987.90   $987.90   $988.00