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 $242.29   3.528%   $250.838   $250.84   $250.85   $250.80  
  Purchase #2 $42.27   5.179%   $44.4592   $44.46   $44.45   $44.50  
  Purchase #3 $227.56   5.754%   $240.6538   $240.65   $240.65   $240.70  
  Purchase #4 $245.63   10.331%   $271.006   $271.01   $271.00   $271.00  
  Purchase #5 $198.84   4.786%   $208.3565   $208.36   $208.35   $208.40  
  Purchase #6 $224.27   8.868%   $244.1583   $244.16   $244.15   $244.20  
  Purchase #7 $138.38   12.168%   $155.2181   $155.22   $155.20   $155.20  
  7 purchase totals = $1,319.24       $1,414.6899   $1,414.70   $1,414.65   $1,414.80