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 $90.54   6.186%   $96.1408   $96.14   $96.15   $96.10  
  Purchase #2 $221.48   12.426%   $249.0011   $249.00   $249.00   $249.00  
  Purchase #3 $59.54   13.129%   $67.357   $67.36   $67.35   $67.40  
  Purchase #4 $202.84   6.822%   $216.6777   $216.68   $216.70   $216.70  
  Purchase #5 $221.87   5.687%   $234.4877   $234.49   $234.50   $234.50  
  Purchase #6 $37.81   6.389%   $40.2257   $40.23   $40.25   $40.20  
  Purchase #7 $146.78   10.520%   $162.2213   $162.22   $162.20   $162.20  
  7 purchase totals = $980.86       $1,066.1113   $1,066.12   $1,066.15   $1,066.10