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 $55.45   6.202%   $58.889   $58.89   $58.90   $58.90  
  Purchase #2 $71.91   10.860%   $79.7194   $79.72   $79.70   $79.70  
  Purchase #3 $174.96   5.471%   $184.5321   $184.53   $184.55   $184.50  
  Purchase #4 $87.57   5.867%   $92.7077   $92.71   $92.70   $92.70  
  Purchase #5 $5.39   11.238%   $5.9957   $6.00   $6.00   $6.00  
  Purchase #6 $105.48   11.667%   $117.7864   $117.79   $117.80   $117.80  
  Purchase #7 $216.31   3.734%   $224.387   $224.39   $224.40   $224.40  
  7 purchase totals = $717.07       $764.0173   $764.03   $764.05   $764.00