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 $46.89   13.593%   $53.2638   $53.26   $53.25   $53.30  
  Purchase #2 $202.85   3.309%   $209.5623   $209.56   $209.55   $209.60  
  Purchase #3 $214.92   7.518%   $231.0777   $231.08   $231.10   $231.10  
  Purchase #4 $193.27   6.171%   $205.1967   $205.20   $205.20   $205.20  
  Purchase #5 $185.34   11.404%   $206.4762   $206.48   $206.50   $206.50  
  Purchase #6 $107.64   10.517%   $118.9605   $118.96   $118.95   $119.00  
  Purchase #7 $10.78   11.387%   $12.0075   $12.01   $12.00   $12.00  
  7 purchase totals = $961.69       $1,036.5447   $1,036.55   $1,036.55   $1,036.70