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 $114.47   10.726%   $126.7481   $126.75   $126.75   $126.70  
  Purchase #2 $137.44   6.125%   $145.8582   $145.86   $145.85   $145.90  
  Purchase #3 $136.70   4.455%   $142.79   $142.79   $142.80   $142.80  
  Purchase #4 $62.31   11.641%   $69.5635   $69.56   $69.55   $69.60  
  Purchase #5 $95.90   10.388%   $105.8621   $105.86   $105.85   $105.90  
  Purchase #6 $242.65   8.761%   $263.9086   $263.91   $263.90   $263.90  
  Purchase #7 $6.40   12.679%   $7.2115   $7.21   $7.20   $7.20  
  7 purchase totals = $795.87       $861.9420   $861.94   $861.90   $862.00