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 $90.65   4.291%   $94.5398   $94.54   $94.55   $94.50  
  Purchase #2 $115.58   9.402%   $126.4468   $126.45   $126.45   $126.40  
  Purchase #3 $219.86   8.167%   $237.816   $237.82   $237.80   $237.80  
  Purchase #4 $183.77   8.469%   $199.3335   $199.33   $199.35   $199.30  
  Purchase #5 $62.59   6.420%   $66.6083   $66.61   $66.60   $66.60  
  Purchase #6 $24.88   5.628%   $26.2802   $26.28   $26.30   $26.30  
  Purchase #7 $158.50   12.189%   $177.8196   $177.82   $177.80   $177.80  
  7 purchase totals = $855.83       $928.8442   $928.85   $928.85   $928.70