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 $102.66   13.218%   $116.2296   $116.23   $116.25   $116.20  
  Purchase #2 $161.58   5.738%   $170.8515   $170.85   $170.85   $170.90  
  Purchase #3 $46.41   3.155%   $47.8742   $47.87   $47.85   $47.90  
  Purchase #4 $215.35   5.531%   $227.261   $227.26   $227.25   $227.30  
  Purchase #5 $79.80   11.707%   $89.1422   $89.14   $89.15   $89.10  
  Purchase #6 $194.86   11.444%   $217.1598   $217.16   $217.15   $217.20  
  Purchase #7 $69.89   7.363%   $75.036   $75.04   $75.05   $75.00  
  7 purchase totals = $870.55       $943.5543   $943.55   $943.55   $943.60