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 $36.42   4.462%   $38.0451   $38.05   $38.05   $38.00  
  Purchase #2 $159.64   9.506%   $174.8154   $174.82   $174.80   $174.80  
  Purchase #3 $208.36   7.629%   $224.2558   $224.26   $224.25   $224.30  
  Purchase #4 $44.98   13.151%   $50.8953   $50.90   $50.90   $50.90  
  Purchase #5 $173.86   3.406%   $179.7817   $179.78   $179.80   $179.80  
  Purchase #6 $19.27   10.780%   $21.3473   $21.35   $21.35   $21.30  
  Purchase #7 $63.71   8.566%   $69.1674   $69.17   $69.15   $69.20  
  7 purchase totals = $706.24       $758.3080   $758.33   $758.30   $758.30