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 $66.51   12.246%   $74.6548   $74.65   $74.65   $74.70  
  Purchase #2 $23.56   13.544%   $26.751   $26.75   $26.75   $26.80  
  Purchase #3 $58.97   8.164%   $63.7843   $63.78   $63.80   $63.80  
  Purchase #4 $114.66   3.109%   $118.2248   $118.22   $118.20   $118.20  
  Purchase #5 $20.32   5.711%   $21.4805   $21.48   $21.50   $21.50  
  Purchase #6 $230.41   9.333%   $251.9142   $251.91   $251.90   $251.90  
  Purchase #7 $73.56   7.143%   $78.8144   $78.81   $78.80   $78.80  
  7 purchase totals = $587.99       $635.6240   $635.60   $635.60   $635.70