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 $245.83   10.572%   $271.8191   $271.82   $271.80   $271.80  
  Purchase #2 $211.87   8.474%   $229.8239   $229.82   $229.80   $229.80  
  Purchase #3 $6.41   11.781%   $7.1652   $7.17   $7.15   $7.20  
  Purchase #4 $51.55   11.185%   $57.3159   $57.32   $57.30   $57.30  
  Purchase #5 $71.98   11.275%   $80.0957   $80.10   $80.10   $80.10  
  Purchase #6 $248.83   3.281%   $256.9941   $256.99   $257.00   $257.00  
  Purchase #7 $192.26   4.465%   $200.8444   $200.84   $200.85   $200.80  
  7 purchase totals = $1,028.73       $1,104.0583   $1,104.06   $1,104.00   $1,104.00