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 $56.77   3.227%   $58.602   $58.60   $58.60   $58.60  
  Purchase #2 $157.81   11.530%   $176.0055   $176.01   $176.00   $176.00  
  Purchase #3 $111.57   11.132%   $123.99   $123.99   $124.00   $124.00  
  Purchase #4 $135.68   9.298%   $148.2955   $148.30   $148.30   $148.30  
  Purchase #5 $65.59   5.198%   $68.9994   $69.00   $69.00   $69.00  
  Purchase #6 $32.75   4.158%   $34.1117   $34.11   $34.10   $34.10  
  Purchase #7 $229.57   7.558%   $246.9209   $246.92   $246.90   $246.90  
  7 purchase totals = $789.74       $856.9250   $856.93   $856.90   $856.90