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 $67.88   11.528%   $75.7052   $75.71   $75.70   $75.70  
  Purchase #2 $233.36   12.131%   $261.6689   $261.67   $261.65   $261.70  
  Purchase #3 $106.65   3.474%   $110.355   $110.36   $110.35   $110.40  
  Purchase #4 $146.83   6.297%   $156.0759   $156.08   $156.10   $156.10  
  Purchase #5 $141.99   7.302%   $152.3581   $152.36   $152.35   $152.40  
  Purchase #6 $232.93   12.577%   $262.2256   $262.23   $262.25   $262.20  
  Purchase #7 $26.49   7.186%   $28.3936   $28.39   $28.40   $28.40  
  7 purchase totals = $956.13       $1,046.7823   $1,046.80   $1,046.80   $1,046.90