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 $232.94   8.567%   $252.896   $252.90   $252.90   $252.90  
  Purchase #2 $115.37   13.499%   $130.9438   $130.94   $130.95   $130.90  
  Purchase #3 $43.95   11.649%   $49.0697   $49.07   $49.05   $49.10  
  Purchase #4 $96.59   3.767%   $100.2285   $100.23   $100.25   $100.20  
  Purchase #5 $150.95   5.644%   $159.4696   $159.47   $159.45   $159.50  
  Purchase #6 $195.31   4.341%   $203.7884   $203.79   $203.80   $203.80  
  Purchase #7 $90.61   5.267%   $95.3824   $95.38   $95.40   $95.40  
  7 purchase totals = $925.72       $991.7784   $991.78   $991.80   $991.80