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 $8.83   13.352%   $10.009   $10.01   $10.00   $10.00  
  Purchase #2 $178.68   8.398%   $193.6855   $193.69   $193.70   $193.70  
  Purchase #3 $22.57   8.831%   $24.5632   $24.56   $24.55   $24.60  
  Purchase #4 $186.81   3.126%   $192.6497   $192.65   $192.65   $192.60  
  Purchase #5 $153.94   3.465%   $159.274   $159.27   $159.25   $159.30  
  Purchase #6 $159.75   13.214%   $180.8594   $180.86   $180.85   $180.90  
  Purchase #7 $5.94   9.475%   $6.5028   $6.50   $6.50   $6.50  
  7 purchase totals = $716.52       $767.5436   $767.54   $767.50   $767.60