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 $141.83   13.297%   $160.6891   $160.69   $160.70   $160.70  
  Purchase #2 $94.92   11.644%   $105.9725   $105.97   $105.95   $106.00  
  Purchase #3 $180.84   7.568%   $194.526   $194.53   $194.55   $194.50  
  Purchase #4 $232.68   3.481%   $240.7796   $240.78   $240.80   $240.80  
  Purchase #5 $172.28   13.462%   $195.4723   $195.47   $195.45   $195.50  
  Purchase #6 $221.67   5.147%   $233.0794   $233.08   $233.10   $233.10  
  Purchase #7 $124.40   13.518%   $141.2164   $141.22   $141.20   $141.20  
  7 purchase totals = $1,168.62       $1,271.7353   $1,271.74   $1,271.75   $1,271.80