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 $166.70   11.856%   $186.464   $186.46   $186.45   $186.50  
  Purchase #2 $194.81   10.870%   $215.9858   $215.99   $216.00   $216.00  
  Purchase #3 $8.55   10.131%   $9.4162   $9.42   $9.40   $9.40  
  Purchase #4 $153.42   11.288%   $170.738   $170.74   $170.75   $170.70  
  Purchase #5 $109.56   5.418%   $115.496   $115.50   $115.50   $115.50  
  Purchase #6 $248.35   9.298%   $271.4416   $271.44   $271.45   $271.40  
  Purchase #7 $60.40   3.671%   $62.6173   $62.62   $62.60   $62.60  
  7 purchase totals = $941.79       $1,032.1589   $1,032.17   $1,032.15   $1,032.10