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 $45.65   4.257%   $47.5933   $47.59   $47.60   $47.60  
  Purchase #2 $234.73   11.309%   $261.2756   $261.28   $261.30   $261.30  
  Purchase #3 $145.29   12.460%   $163.3931   $163.39   $163.40   $163.40  
  Purchase #4 $202.65   11.827%   $226.6174   $226.62   $226.60   $226.60  
  Purchase #5 $223.36   12.405%   $251.0678   $251.07   $251.05   $251.10  
  Purchase #6 $228.97   10.628%   $253.3049   $253.30   $253.30   $253.30  
  Purchase #7 $159.96   11.501%   $178.357   $178.36   $178.35   $178.40  
  7 purchase totals = $1,240.61       $1,381.6091   $1,381.61   $1,381.60   $1,381.70