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 $206.35   12.745%   $232.6493   $232.65   $232.65   $232.60  
  Purchase #2 $214.53   3.224%   $221.4464   $221.45   $221.45   $221.40  
  Purchase #3 $227.35   7.491%   $244.3808   $244.38   $244.40   $244.40  
  Purchase #4 $156.29   6.703%   $166.7661   $166.77   $166.75   $166.80  
  Purchase #5 $68.35   9.261%   $74.6799   $74.68   $74.70   $74.70  
  Purchase #6 $136.74   3.377%   $141.3577   $141.36   $141.35   $141.40  
  Purchase #7 $142.92   8.696%   $155.3483   $155.35   $155.35   $155.30  
  7 purchase totals = $1,152.53       $1,236.6285   $1,236.64   $1,236.65   $1,236.60