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 $244.60   11.733%   $273.2989   $273.30   $273.30   $273.30  
  Purchase #2 $59.98   13.108%   $67.8422   $67.84   $67.85   $67.80  
  Purchase #3 $74.96   12.147%   $84.0654   $84.07   $84.05   $84.10  
  Purchase #4 $178.96   6.108%   $189.8909   $189.89   $189.90   $189.90  
  Purchase #5 $212.73   10.238%   $234.5093   $234.51   $234.50   $234.50  
  Purchase #6 $202.65   11.358%   $225.667   $225.67   $225.65   $225.70  
  Purchase #7 $69.77   4.484%   $72.8985   $72.90   $72.90   $72.90  
  7 purchase totals = $1,043.65       $1,148.1722   $1,148.18   $1,148.15   $1,148.20