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 $23.53   10.358%   $25.9672   $25.97   $25.95   $26.00  
  Purchase #2 $154.60   13.561%   $175.5653   $175.57   $175.55   $175.60  
  Purchase #3 $152.51   9.682%   $167.276   $167.28   $167.30   $167.30  
  Purchase #4 $248.71   13.774%   $282.9673   $282.97   $282.95   $283.00  
  Purchase #5 $104.86   5.836%   $110.9796   $110.98   $111.00   $111.00  
  Purchase #6 $88.98   10.354%   $98.193   $98.19   $98.20   $98.20  
  Purchase #7 $8.78   9.699%   $9.6316   $9.63   $9.65   $9.60  
  7 purchase totals = $781.97       $870.5800   $870.59   $870.60   $870.70