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 $204.73   4.796%   $214.5489   $214.55   $214.55   $214.50  
  Purchase #2 $106.42   11.798%   $118.9754   $118.98   $119.00   $119.00  
  Purchase #3 $167.66   3.338%   $173.2565   $173.26   $173.25   $173.30  
  Purchase #4 $208.59   9.374%   $228.1432   $228.14   $228.15   $228.10  
  Purchase #5 $196.27   13.419%   $222.6075   $222.61   $222.60   $222.60  
  Purchase #6 $153.99   12.218%   $172.8045   $172.80   $172.80   $172.80  
  Purchase #7 $191.86   7.356%   $205.9732   $205.97   $205.95   $206.00  
  7 purchase totals = $1,229.52       $1,336.3092   $1,336.31   $1,336.30   $1,336.30