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 $88.86   4.860%   $93.1786   $93.18   $93.20   $93.20  
  Purchase #2 $153.58   13.221%   $173.8848   $173.88   $173.90   $173.90  
  Purchase #3 $35.82   6.619%   $38.1909   $38.19   $38.20   $38.20  
  Purchase #4 $88.39   3.636%   $91.6039   $91.60   $91.60   $91.60  
  Purchase #5 $241.64   12.267%   $271.282   $271.28   $271.30   $271.30  
  Purchase #6 $202.93   10.657%   $224.5563   $224.56   $224.55   $224.60  
  Purchase #7 $144.53   5.116%   $151.9242   $151.92   $151.90   $151.90  
  7 purchase totals = $955.75       $1,044.6207   $1,044.61   $1,044.65   $1,044.70