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 $226.98   12.807%   $256.0493   $256.05   $256.05   $256.00  
  Purchase #2 $204.32   10.144%   $225.0462   $225.05   $225.05   $225.00  
  Purchase #3 $161.84   13.320%   $183.3971   $183.40   $183.40   $183.40  
  Purchase #4 $182.50   3.492%   $188.8729   $188.87   $188.85   $188.90  
  Purchase #5 $36.44   8.566%   $39.5615   $39.56   $39.55   $39.60  
  Purchase #6 $213.36   11.184%   $237.2222   $237.22   $237.20   $237.20  
  Purchase #7 $105.55   13.222%   $119.5058   $119.51   $119.50   $119.50  
  7 purchase totals = $1,130.99       $1,249.6550   $1,249.66   $1,249.60   $1,249.60