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 $30.93   8.309%   $33.5   $33.50   $33.50   $33.50  
  Purchase #2 $209.67   5.178%   $220.5267   $220.53   $220.55   $220.50  
  Purchase #3 $157.74   13.312%   $178.7383   $178.74   $178.75   $178.70  
  Purchase #4 $214.94   11.810%   $240.3244   $240.32   $240.30   $240.30  
  Purchase #5 $215.94   6.267%   $229.473   $229.47   $229.45   $229.50  
  Purchase #6 $38.46   3.294%   $39.7269   $39.73   $39.75   $39.70  
  Purchase #7 $176.45   4.157%   $183.785   $183.79   $183.80   $183.80  
  7 purchase totals = $1,044.13       $1,126.0743   $1,126.08   $1,126.10   $1,126.00