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 $64.57   9.499%   $70.7035   $70.70   $70.70   $70.70  
  Purchase #2 $245.35   11.697%   $274.0486   $274.05   $274.05   $274.00  
  Purchase #3 $217.98   8.582%   $236.687   $236.69   $236.70   $236.70  
  Purchase #4 $144.98   9.832%   $159.2344   $159.23   $159.25   $159.20  
  Purchase #5 $216.94   11.656%   $242.2265   $242.23   $242.25   $242.20  
  Purchase #6 $63.73   4.735%   $66.7476   $66.75   $66.75   $66.70  
  Purchase #7 $194.30   8.399%   $210.6193   $210.62   $210.60   $210.60  
  7 purchase totals = $1,147.85       $1,260.2669   $1,260.27   $1,260.30   $1,260.10