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 $60.26   10.232%   $66.4258   $66.43   $66.45   $66.40  
  Purchase #2 $226.67   12.612%   $255.2576   $255.26   $255.25   $255.30  
  Purchase #3 $161.40   8.812%   $175.6226   $175.62   $175.60   $175.60  
  Purchase #4 $153.85   13.496%   $174.6136   $174.61   $174.60   $174.60  
  Purchase #5 $223.57   4.741%   $234.1695   $234.17   $234.15   $234.20  
  Purchase #6 $130.33   6.445%   $138.7298   $138.73   $138.75   $138.70  
  Purchase #7 $151.80   4.602%   $158.7858   $158.79   $158.80   $158.80  
  7 purchase totals = $1,107.88       $1,203.6047   $1,203.61   $1,203.60   $1,203.60