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 $24.51   9.191%   $26.7627   $26.76   $26.75   $26.80  
  Purchase #2 $204.76   11.206%   $227.7054   $227.71   $227.70   $227.70  
  Purchase #3 $97.27   13.213%   $110.1223   $110.12   $110.10   $110.10  
  Purchase #4 $158.51   8.242%   $171.5744   $171.57   $171.55   $171.60  
  Purchase #5 $105.78   7.574%   $113.7918   $113.79   $113.80   $113.80  
  Purchase #6 $240.61   10.490%   $265.85   $265.85   $265.85   $265.90  
  Purchase #7 $50.80   13.492%   $57.6539   $57.65   $57.65   $57.70  
  7 purchase totals = $882.24       $973.4605   $973.45   $973.40   $973.60