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 $118.93   4.569%   $124.3639   $124.36   $124.35   $124.40  
  Purchase #2 $140.64   10.691%   $155.6758   $155.68   $155.70   $155.70  
  Purchase #3 $225.93   6.169%   $239.8676   $239.87   $239.85   $239.90  
  Purchase #4 $98.40   9.372%   $107.622   $107.62   $107.60   $107.60  
  Purchase #5 $189.54   8.269%   $205.2131   $205.21   $205.20   $205.20  
  Purchase #6 $221.55   11.836%   $247.7727   $247.77   $247.75   $247.80  
  Purchase #7 $224.56   8.250%   $243.0862   $243.09   $243.10   $243.10  
  7 purchase totals = $1,219.55       $1,323.6013   $1,323.60   $1,323.55   $1,323.70