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 $32.67   5.802%   $34.5655   $34.57   $34.55   $34.60  
  Purchase #2 $219.61   11.434%   $244.7202   $244.72   $244.70   $244.70  
  Purchase #3 $23.64   13.438%   $26.8167   $26.82   $26.80   $26.80  
  Purchase #4 $50.88   6.859%   $54.3699   $54.37   $54.35   $54.40  
  Purchase #5 $239.67   7.302%   $257.1707   $257.17   $257.15   $257.20  
  Purchase #6 $99.40   9.708%   $109.0498   $109.05   $109.05   $109.00  
  Purchase #7 $66.74   7.620%   $71.8256   $71.83   $71.85   $71.80  
  7 purchase totals = $732.61       $798.5184   $798.53   $798.45   $798.50