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 $50.43   5.165%   $53.0347   $53.03   $53.05   $53.00  
  Purchase #2 $170.89   12.327%   $191.9556   $191.96   $191.95   $192.00  
  Purchase #3 $118.40   12.680%   $133.4131   $133.41   $133.40   $133.40  
  Purchase #4 $234.34   13.501%   $265.9782   $265.98   $266.00   $266.00  
  Purchase #5 $233.67   10.544%   $258.3082   $258.31   $258.30   $258.30  
  Purchase #6 $92.80   4.272%   $96.7644   $96.76   $96.75   $96.80  
  Purchase #7 $239.78   8.695%   $260.6289   $260.63   $260.65   $260.60  
  7 purchase totals = $1,140.31       $1,260.0831   $1,260.08   $1,260.10   $1,260.10