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 $6.84   3.480%   $7.078   $7.08   $7.10   $7.10  
  Purchase #2 $101.90   7.109%   $109.1441   $109.14   $109.15   $109.10  
  Purchase #3 $242.91   12.122%   $272.3556   $272.36   $272.35   $272.40  
  Purchase #4 $238.48   4.534%   $249.2927   $249.29   $249.30   $249.30  
  Purchase #5 $219.85   7.686%   $236.7477   $236.75   $236.75   $236.70  
  Purchase #6 $178.43   12.153%   $200.1146   $200.11   $200.10   $200.10  
  Purchase #7 $107.67   12.675%   $121.3172   $121.32   $121.30   $121.30  
  7 purchase totals = $1,096.08       $1,196.0499   $1,196.05   $1,196.05   $1,196.00