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 $33.49   6.319%   $35.6062   $35.61   $35.60   $35.60  
  Purchase #2 $235.63   13.192%   $266.7143   $266.71   $266.70   $266.70  
  Purchase #3 $105.51   3.669%   $109.3812   $109.38   $109.40   $109.40  
  Purchase #4 $229.29   3.523%   $237.3679   $237.37   $237.35   $237.40  
  Purchase #5 $167.96   3.697%   $174.1695   $174.17   $174.15   $174.20  
  Purchase #6 $26.73   5.682%   $28.2488   $28.25   $28.25   $28.20  
  Purchase #7 $200.55   9.336%   $219.2733   $219.27   $219.25   $219.30  
  7 purchase totals = $999.16       $1,070.7612   $1,070.76   $1,070.70   $1,070.80