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 $246.83   5.679%   $260.8475   $260.85   $260.85   $260.80  
  Purchase #2 $110.97   7.391%   $119.1718   $119.17   $119.15   $119.20  
  Purchase #3 $12.79   9.466%   $14.0007   $14.00   $14.00   $14.00  
  Purchase #4 $242.84   3.452%   $251.2228   $251.22   $251.20   $251.20  
  Purchase #5 $109.26   4.476%   $114.1505   $114.15   $114.15   $114.20  
  Purchase #6 $13.28   7.638%   $14.2943   $14.29   $14.30   $14.30  
  Purchase #7 $221.80   10.677%   $245.4816   $245.48   $245.50   $245.50  
  7 purchase totals = $957.77       $1,019.1692   $1,019.16   $1,019.15   $1,019.20