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 $110.71   12.205%   $124.2222   $124.22   $124.20   $124.20  
  Purchase #2 $202.32   10.531%   $223.6263   $223.63   $223.65   $223.60  
  Purchase #3 $236.97   9.164%   $258.6859   $258.69   $258.70   $258.70  
  Purchase #4 $133.97   13.378%   $151.8925   $151.89   $151.90   $151.90  
  Purchase #5 $228.51   9.762%   $250.8171   $250.82   $250.80   $250.80  
  Purchase #6 $106.94   9.534%   $117.1357   $117.14   $117.15   $117.10  
  Purchase #7 $95.82   10.825%   $106.1925   $106.19   $106.20   $106.20  
  7 purchase totals = $1,115.24       $1,232.5722   $1,232.58   $1,232.60   $1,232.50