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 $241.37   3.537%   $249.9073   $249.91   $249.90   $249.90  
  Purchase #2 $61.62   5.674%   $65.1163   $65.12   $65.10   $65.10  
  Purchase #3 $29.83   3.422%   $30.8508   $30.85   $30.85   $30.90  
  Purchase #4 $236.81   13.370%   $268.4715   $268.47   $268.45   $268.50  
  Purchase #5 $142.43   12.678%   $160.4873   $160.49   $160.50   $160.50  
  Purchase #6 $206.68   6.661%   $220.447   $220.45   $220.45   $220.40  
  Purchase #7 $59.91   8.354%   $64.9149   $64.91   $64.90   $64.90  
  7 purchase totals = $978.65       $1,060.1951   $1,060.20   $1,060.15   $1,060.20