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 $203.81   10.694%   $225.6054   $225.61   $225.60   $225.60  
  Purchase #2 $235.49   3.528%   $243.7981   $243.80   $243.80   $243.80  
  Purchase #3 $227.75   11.516%   $253.9777   $253.98   $254.00   $254.00  
  Purchase #4 $98.97   5.819%   $104.7291   $104.73   $104.75   $104.70  
  Purchase #5 $46.74   6.566%   $49.8089   $49.81   $49.80   $49.80  
  Purchase #6 $175.93   6.793%   $187.8809   $187.88   $187.90   $187.90  
  Purchase #7 $237.77   10.511%   $262.762   $262.76   $262.75   $262.80  
  7 purchase totals = $1,226.46       $1,328.5621   $1,328.57   $1,328.60   $1,328.60