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 $178.65   8.632%   $194.0711   $194.07   $194.05   $194.10  
  Purchase #2 $219.92   11.145%   $244.4301   $244.43   $244.45   $244.40  
  Purchase #3 $133.88   5.823%   $141.6758   $141.68   $141.70   $141.70  
  Purchase #4 $194.29   11.868%   $217.3483   $217.35   $217.35   $217.30  
  Purchase #5 $26.91   13.699%   $30.5964   $30.60   $30.60   $30.60  
  Purchase #6 $205.58   10.242%   $226.6355   $226.64   $226.65   $226.60  
  Purchase #7 $61.54   7.535%   $66.177   $66.18   $66.20   $66.20  
  7 purchase totals = $1,020.77       $1,120.9342   $1,120.95   $1,121.00   $1,120.90