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 $172.96   13.799%   $196.8268   $196.83   $196.85   $196.80  
  Purchase #2 $210.77   7.116%   $225.7684   $225.77   $225.75   $225.80  
  Purchase #3 $98.82   3.719%   $102.4951   $102.50   $102.50   $102.50  
  Purchase #4 $141.74   8.357%   $153.5852   $153.59   $153.60   $153.60  
  Purchase #5 $18.92   4.440%   $19.76   $19.76   $19.75   $19.80  
  Purchase #6 $5.66   11.691%   $6.3217   $6.32   $6.30   $6.30  
  Purchase #7 $226.37   11.327%   $252.0109   $252.01   $252.00   $252.00  
  7 purchase totals = $875.24       $956.7681   $956.78   $956.75   $956.80