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 $104.53   11.452%   $116.5008   $116.50   $116.50   $116.50  
  Purchase #2 $6.60   5.233%   $6.9454   $6.95   $6.95   $6.90  
  Purchase #3 $167.67   9.174%   $183.052   $183.05   $183.05   $183.10  
  Purchase #4 $92.37   11.519%   $103.0101   $103.01   $103.00   $103.00  
  Purchase #5 $147.69   8.309%   $159.9616   $159.96   $159.95   $160.00  
  Purchase #6 $250.26   4.569%   $261.6944   $261.69   $261.70   $261.70  
  Purchase #7 $172.59   12.841%   $194.7523   $194.75   $194.75   $194.80  
  7 purchase totals = $941.71       $1,025.9166   $1,025.91   $1,025.90   $1,026.00