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 $169.98   7.259%   $182.3188   $182.32   $182.30   $182.30  
  Purchase #2 $210.58   4.171%   $219.3633   $219.36   $219.35   $219.40  
  Purchase #3 $19.43   6.738%   $20.7392   $20.74   $20.75   $20.70  
  Purchase #4 $83.89   11.391%   $93.4459   $93.45   $93.45   $93.40  
  Purchase #5 $104.92   11.669%   $117.1631   $117.16   $117.15   $117.20  
  Purchase #6 $199.67   7.471%   $214.5873   $214.59   $214.60   $214.60  
  Purchase #7 $138.79   11.254%   $154.4094   $154.41   $154.40   $154.40  
  7 purchase totals = $927.26       $1,002.0270   $1,002.03   $1,002.00   $1,002.00