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 $204.94   8.820%   $223.0157   $223.02   $223.00   $223.00  
  Purchase #2 $94.56   4.230%   $98.5599   $98.56   $98.55   $98.60  
  Purchase #3 $92.43   3.843%   $95.9821   $95.98   $96.00   $96.00  
  Purchase #4 $242.60   11.812%   $271.2559   $271.26   $271.25   $271.30  
  Purchase #5 $227.61   6.128%   $241.5579   $241.56   $241.55   $241.60  
  Purchase #6 $234.42   13.206%   $265.3775   $265.38   $265.40   $265.40  
  Purchase #7 $241.96   9.537%   $265.0357   $265.04   $265.05   $265.00  
  7 purchase totals = $1,338.52       $1,460.7847   $1,460.80   $1,460.80   $1,460.90