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 $242.34   11.222%   $269.5354   $269.54   $269.55   $269.50  
  Purchase #2 $232.60   3.667%   $241.1294   $241.13   $241.15   $241.10  
  Purchase #3 $248.26   3.519%   $256.9963   $257.00   $257.00   $257.00  
  Purchase #4 $183.90   11.496%   $205.0411   $205.04   $205.05   $205.00  
  Purchase #5 $95.95   8.793%   $104.3869   $104.39   $104.40   $104.40  
  Purchase #6 $245.74   8.447%   $266.4977   $266.50   $266.50   $266.50  
  Purchase #7 $5.65   5.813%   $5.9784   $5.98   $6.00   $6.00  
  7 purchase totals = $1,254.44       $1,349.5652   $1,349.58   $1,349.65   $1,349.50