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 $67.73   6.175%   $71.9123   $71.91   $71.90   $71.90  
  Purchase #2 $228.69   7.538%   $245.9287   $245.93   $245.95   $245.90  
  Purchase #3 $119.57   5.172%   $125.7542   $125.75   $125.75   $125.80  
  Purchase #4 $74.41   5.153%   $78.2443   $78.24   $78.25   $78.20  
  Purchase #5 $126.83   11.811%   $141.8099   $141.81   $141.80   $141.80  
  Purchase #6 $16.49   9.420%   $18.0434   $18.04   $18.05   $18.00  
  Purchase #7 $68.84   8.552%   $74.7272   $74.73   $74.75   $74.70  
  7 purchase totals = $702.56       $756.4200   $756.41   $756.45   $756.30