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 $183.69   11.545%   $204.897   $204.90   $204.90   $204.90  
  Purchase #2 $210.56   7.535%   $226.4257   $226.43   $226.45   $226.40  
  Purchase #3 $91.71   13.554%   $104.1404   $104.14   $104.15   $104.10  
  Purchase #4 $60.98   11.827%   $68.1921   $68.19   $68.20   $68.20  
  Purchase #5 $247.79   9.646%   $271.6918   $271.69   $271.70   $271.70  
  Purchase #6 $119.56   3.336%   $123.5485   $123.55   $123.55   $123.50  
  Purchase #7 $22.29   11.643%   $24.8852   $24.89   $24.90   $24.90  
  7 purchase totals = $936.58       $1,023.7807   $1,023.79   $1,023.85   $1,023.70