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 $111.37   5.186%   $117.1456   $117.15   $117.15   $117.10  
  Purchase #2 $51.93   3.331%   $53.6598   $53.66   $53.65   $53.70  
  Purchase #3 $76.70   8.170%   $82.9664   $82.97   $82.95   $83.00  
  Purchase #4 $95.43   10.777%   $105.7145   $105.71   $105.70   $105.70  
  Purchase #5 $91.79   5.215%   $96.5768   $96.58   $96.60   $96.60  
  Purchase #6 $112.54   5.725%   $118.9829   $118.98   $119.00   $119.00  
  Purchase #7 $116.91   11.349%   $130.1781   $130.18   $130.20   $130.20  
  7 purchase totals = $656.67       $705.2241   $705.23   $705.25   $705.30