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 $229.87   13.610%   $261.1553   $261.16   $261.15   $261.20  
  Purchase #2 $163.38   5.274%   $171.9967   $172.00   $172.00   $172.00  
  Purchase #3 $149.62   7.363%   $160.6365   $160.64   $160.65   $160.60  
  Purchase #4 $166.97   13.622%   $189.7147   $189.71   $189.70   $189.70  
  Purchase #5 $93.88   11.251%   $104.4424   $104.44   $104.45   $104.40  
  Purchase #6 $99.33   8.593%   $107.8654   $107.87   $107.85   $107.90  
  Purchase #7 $34.38   10.745%   $38.0741   $38.07   $38.05   $38.10  
  7 purchase totals = $937.43       $1,033.8851   $1,033.89   $1,033.85   $1,033.90