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 $89.97   3.569%   $93.181   $93.18   $93.20   $93.20  
  Purchase #2 $206.73   12.139%   $231.825   $231.83   $231.85   $231.80  
  Purchase #3 $90.39   13.558%   $102.6451   $102.65   $102.65   $102.60  
  Purchase #4 $158.55   12.541%   $178.4338   $178.43   $178.45   $178.40  
  Purchase #5 $43.62   10.546%   $48.2202   $48.22   $48.20   $48.20  
  Purchase #6 $106.74   8.457%   $115.767   $115.77   $115.75   $115.80  
  Purchase #7 $186.85   4.383%   $195.0396   $195.04   $195.05   $195.00  
  7 purchase totals = $882.85       $965.1117   $965.12   $965.15   $965.00