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 $85.80   12.123%   $96.2015   $96.20   $96.20   $96.20  
  Purchase #2 $231.27   11.242%   $257.2694   $257.27   $257.25   $257.30  
  Purchase #3 $107.72   9.860%   $118.3412   $118.34   $118.35   $118.30  
  Purchase #4 $160.25   12.731%   $180.6514   $180.65   $180.65   $180.70  
  Purchase #5 $26.76   10.364%   $29.5334   $29.53   $29.55   $29.50  
  Purchase #6 $141.65   3.252%   $146.2565   $146.26   $146.25   $146.30  
  Purchase #7 $219.62   11.383%   $244.6193   $244.62   $244.60   $244.60  
  7 purchase totals = $973.07       $1,072.8727   $1,072.87   $1,072.85   $1,072.90