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 $161.54   13.720%   $183.7033   $183.70   $183.70   $183.70  
  Purchase #2 $189.72   13.218%   $214.7972   $214.80   $214.80   $214.80  
  Purchase #3 $217.71   3.163%   $224.5962   $224.60   $224.60   $224.60  
  Purchase #4 $193.78   7.170%   $207.674   $207.67   $207.65   $207.70  
  Purchase #5 $250.62   10.498%   $276.9301   $276.93   $276.95   $276.90  
  Purchase #6 $137.74   9.798%   $151.2358   $151.24   $151.25   $151.20  
  Purchase #7 $90.84   6.248%   $96.5157   $96.52   $96.50   $96.50  
  7 purchase totals = $1,241.95       $1,355.4523   $1,355.46   $1,355.45   $1,355.40