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 $24.33   9.411%   $26.6197   $26.62   $26.60   $26.60  
  Purchase #2 $223.85   12.261%   $251.2962   $251.30   $251.30   $251.30  
  Purchase #3 $149.75   12.829%   $168.9614   $168.96   $168.95   $169.00  
  Purchase #4 $99.80   12.674%   $112.4487   $112.45   $112.45   $112.40  
  Purchase #5 $199.43   7.678%   $214.7422   $214.74   $214.75   $214.70  
  Purchase #6 $81.90   12.264%   $91.9442   $91.94   $91.95   $91.90  
  Purchase #7 $232.86   5.478%   $245.6161   $245.62   $245.60   $245.60  
  7 purchase totals = $1,011.92       $1,111.6285   $1,111.63   $1,111.60   $1,111.50