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 $215.45   4.742%   $225.6666   $225.67   $225.65   $225.70  
  Purchase #2 $202.29   9.197%   $220.8946   $220.89   $220.90   $220.90  
  Purchase #3 $211.46   7.449%   $227.2117   $227.21   $227.20   $227.20  
  Purchase #4 $183.76   13.456%   $208.4867   $208.49   $208.50   $208.50  
  Purchase #5 $21.45   5.512%   $22.6323   $22.63   $22.65   $22.60  
  Purchase #6 $177.96   6.554%   $189.6235   $189.62   $189.60   $189.60  
  Purchase #7 $144.82   10.869%   $160.5605   $160.56   $160.55   $160.60  
  7 purchase totals = $1,157.19       $1,255.0759   $1,255.07   $1,255.05   $1,255.10