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 $117.81   13.733%   $133.9888   $133.99   $134.00   $134.00  
  Purchase #2 $153.67   5.121%   $161.5394   $161.54   $161.55   $161.50  
  Purchase #3 $46.85   11.280%   $52.1347   $52.13   $52.15   $52.10  
  Purchase #4 $175.75   3.249%   $181.4601   $181.46   $181.45   $181.50  
  Purchase #5 $238.46   9.575%   $261.2925   $261.29   $261.30   $261.30  
  Purchase #6 $249.86   12.226%   $280.4079   $280.41   $280.40   $280.40  
  Purchase #7 $50.76   7.685%   $54.6609   $54.66   $54.65   $54.70  
  7 purchase totals = $1,033.16       $1,125.4843   $1,125.48   $1,125.50   $1,125.50