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 $96.77   9.128%   $105.6032   $105.60   $105.60   $105.60  
  Purchase #2 $111.26   7.589%   $119.7035   $119.70   $119.70   $119.70  
  Purchase #3 $240.48   6.309%   $255.6519   $255.65   $255.65   $255.70  
  Purchase #4 $77.61   12.362%   $87.2041   $87.20   $87.20   $87.20  
  Purchase #5 $168.96   3.592%   $175.029   $175.03   $175.05   $175.00  
  Purchase #6 $162.43   8.548%   $176.3145   $176.31   $176.30   $176.30  
  Purchase #7 $98.42   4.631%   $102.9778   $102.98   $103.00   $103.00  
  7 purchase totals = $955.93       $1,022.4840   $1,022.47   $1,022.50   $1,022.50