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 $195.62   13.130%   $221.3049   $221.30   $221.30   $221.30  
  Purchase #2 $145.25   12.249%   $163.0417   $163.04   $163.05   $163.00  
  Purchase #3 $33.49   12.218%   $37.5818   $37.58   $37.60   $37.60  
  Purchase #4 $166.69   9.716%   $182.8856   $182.89   $182.90   $182.90  
  Purchase #5 $140.32   3.286%   $144.9309   $144.93   $144.95   $144.90  
  Purchase #6 $247.46   4.594%   $258.8283   $258.83   $258.85   $258.80  
  Purchase #7 $94.96   12.165%   $106.5119   $106.51   $106.50   $106.50  
  7 purchase totals = $1,023.79       $1,115.0851   $1,115.08   $1,115.15   $1,115.00