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 $205.52   7.170%   $220.2558   $220.26   $220.25   $220.30  
  Purchase #2 $19.29   3.234%   $19.9138   $19.91   $19.90   $19.90  
  Purchase #3 $29.95   8.688%   $32.5521   $32.55   $32.55   $32.60  
  Purchase #4 $161.56   9.415%   $176.7709   $176.77   $176.75   $176.80  
  Purchase #5 $84.50   6.192%   $89.7322   $89.73   $89.75   $89.70  
  Purchase #6 $242.73   10.488%   $268.1875   $268.19   $268.20   $268.20  
  Purchase #7 $224.78   5.339%   $236.781   $236.78   $236.80   $236.80  
  7 purchase totals = $968.33       $1,044.1933   $1,044.19   $1,044.20   $1,044.30