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 $198.46   8.212%   $214.7575   $214.76   $214.75   $214.80  
  Purchase #2 $65.28   6.226%   $69.3443   $69.34   $69.35   $69.30  
  Purchase #3 $150.57   5.352%   $158.6285   $158.63   $158.65   $158.60  
  Purchase #4 $233.35   5.580%   $246.3709   $246.37   $246.35   $246.40  
  Purchase #5 $32.53   10.273%   $35.8718   $35.87   $35.85   $35.90  
  Purchase #6 $26.73   4.360%   $27.8954   $27.90   $27.90   $27.90  
  Purchase #7 $240.95   12.846%   $271.9024   $271.90   $271.90   $271.90  
  7 purchase totals = $947.87       $1,024.7708   $1,024.77   $1,024.75   $1,024.80