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 $68.94   9.558%   $75.5293   $75.53   $75.55   $75.50  
  Purchase #2 $21.99   10.819%   $24.3691   $24.37   $24.35   $24.40  
  Purchase #3 $206.53   7.654%   $222.3378   $222.34   $222.35   $222.30  
  Purchase #4 $215.69   6.594%   $229.9126   $229.91   $229.90   $229.90  
  Purchase #5 $249.66   10.177%   $275.0679   $275.07   $275.05   $275.10  
  Purchase #6 $210.88   13.578%   $239.5133   $239.51   $239.50   $239.50  
  Purchase #7 $53.75   12.367%   $60.3973   $60.40   $60.40   $60.40  
  7 purchase totals = $1,027.44       $1,127.1273   $1,127.13   $1,127.10   $1,127.10