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 $54.41   13.149%   $61.5644   $61.56   $61.55   $61.60  
  Purchase #2 $231.37   9.444%   $253.2206   $253.22   $253.20   $253.20  
  Purchase #3 $22.95   6.233%   $24.3805   $24.38   $24.40   $24.40  
  Purchase #4 $94.57   10.134%   $104.1537   $104.15   $104.15   $104.20  
  Purchase #5 $169.67   6.756%   $181.1329   $181.13   $181.15   $181.10  
  Purchase #6 $12.38   8.286%   $13.4058   $13.41   $13.40   $13.40  
  Purchase #7 $126.44   13.323%   $143.2856   $143.29   $143.30   $143.30  
  7 purchase totals = $711.79       $781.1435   $781.14   $781.15   $781.20