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 $67.90   8.124%   $73.4162   $73.42   $73.40   $73.40  
  Purchase #2 $96.93   7.730%   $104.4227   $104.42   $104.40   $104.40  
  Purchase #3 $101.89   8.675%   $110.729   $110.73   $110.75   $110.70  
  Purchase #4 $246.67   9.861%   $270.9941   $270.99   $271.00   $271.00  
  Purchase #5 $118.80   13.202%   $134.484   $134.48   $134.50   $134.50  
  Purchase #6 $205.47   11.824%   $229.7648   $229.76   $229.75   $229.80  
  Purchase #7 $75.45   12.206%   $84.6594   $84.66   $84.65   $84.70  
  7 purchase totals = $913.11       $1,008.4702   $1,008.46   $1,008.45   $1,008.50