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 $88.53   10.145%   $97.5114   $97.51   $97.50   $97.50  
  Purchase #2 $214.83   10.721%   $237.8619   $237.86   $237.85   $237.90  
  Purchase #3 $59.61   3.121%   $61.4704   $61.47   $61.45   $61.50  
  Purchase #4 $145.94   3.619%   $151.2216   $151.22   $151.20   $151.20  
  Purchase #5 $201.89   11.173%   $224.4472   $224.45   $224.45   $224.40  
  Purchase #6 $194.65   11.177%   $216.406   $216.41   $216.40   $216.40  
  Purchase #7 $220.42   10.206%   $242.9161   $242.92   $242.90   $242.90  
  7 purchase totals = $1,125.87       $1,231.8346   $1,231.84   $1,231.75   $1,231.80