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 $53.42   12.166%   $59.9191   $59.92   $59.90   $59.90  
  Purchase #2 $222.58   5.430%   $234.6661   $234.67   $234.65   $234.70  
  Purchase #3 $212.73   13.153%   $240.7104   $240.71   $240.70   $240.70  
  Purchase #4 $30.69   4.579%   $32.0953   $32.10   $32.10   $32.10  
  Purchase #5 $208.38   3.222%   $215.094   $215.09   $215.10   $215.10  
  Purchase #6 $200.44   9.636%   $219.7544   $219.75   $219.75   $219.80  
  Purchase #7 $15.78   7.719%   $16.9981   $17.00   $17.00   $17.00  
  7 purchase totals = $944.02       $1,019.2374   $1,019.24   $1,019.20   $1,019.30