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 $60.91   11.164%   $67.71   $67.71   $67.70   $67.70  
  Purchase #2 $23.79   9.341%   $26.0122   $26.01   $26.00   $26.00  
  Purchase #3 $152.79   12.371%   $171.6917   $171.69   $171.70   $171.70  
  Purchase #4 $239.64   10.375%   $264.5027   $264.50   $264.50   $264.50  
  Purchase #5 $90.75   4.142%   $94.5089   $94.51   $94.50   $94.50  
  Purchase #6 $215.94   13.305%   $244.6708   $244.67   $244.65   $244.70  
  Purchase #7 $54.87   11.762%   $61.3238   $61.32   $61.30   $61.30  
  7 purchase totals = $838.69       $930.4201   $930.41   $930.35   $930.40