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 $92.82   13.191%   $105.0639   $105.06   $105.05   $105.10  
  Purchase #2 $100.27   8.704%   $108.9975   $109.00   $109.00   $109.00  
  Purchase #3 $142.68   11.115%   $158.5389   $158.54   $158.55   $158.50  
  Purchase #4 $195.87   12.607%   $220.5633   $220.56   $220.55   $220.60  
  Purchase #5 $79.25   9.797%   $87.0141   $87.01   $87.00   $87.00  
  Purchase #6 $228.95   7.222%   $245.4848   $245.48   $245.50   $245.50  
  Purchase #7 $93.79   4.532%   $98.0406   $98.04   $98.05   $98.00  
  7 purchase totals = $933.63       $1,023.7031   $1,023.69   $1,023.70   $1,023.70