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 $156.60   5.378%   $165.0219   $165.02   $165.00   $165.00  
  Purchase #2 $228.25   11.712%   $254.9826   $254.98   $255.00   $255.00  
  Purchase #3 $246.48   10.111%   $271.4016   $271.40   $271.40   $271.40  
  Purchase #4 $197.61   8.204%   $213.8219   $213.82   $213.80   $213.80  
  Purchase #5 $202.95   11.462%   $226.2121   $226.21   $226.20   $226.20  
  Purchase #6 $95.50   3.578%   $98.917   $98.92   $98.90   $98.90  
  Purchase #7 $241.91   9.834%   $265.6994   $265.70   $265.70   $265.70  
  7 purchase totals = $1,369.30       $1,496.0565   $1,496.05   $1,496.00   $1,496.00