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 $214.65   6.137%   $227.8231   $227.82   $227.80   $227.80  
  Purchase #2 $110.74   5.328%   $116.6402   $116.64   $116.65   $116.60  
  Purchase #3 $100.39   12.286%   $112.7239   $112.72   $112.70   $112.70  
  Purchase #4 $159.38   8.608%   $173.0994   $173.10   $173.10   $173.10  
  Purchase #5 $126.35   3.635%   $130.9428   $130.94   $130.95   $130.90  
  Purchase #6 $45.48   11.284%   $50.612   $50.61   $50.60   $50.60  
  Purchase #7 $164.97   10.184%   $181.7705   $181.77   $181.75   $181.80  
  7 purchase totals = $921.96       $993.6119   $993.60   $993.55   $993.50