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 $68.89   11.150%   $76.5712   $76.57   $76.55   $76.60  
  Purchase #2 $16.77   12.574%   $18.8787   $18.88   $18.90   $18.90  
  Purchase #3 $179.78   7.229%   $192.7763   $192.78   $192.80   $192.80  
  Purchase #4 $183.86   7.304%   $197.2891   $197.29   $197.30   $197.30  
  Purchase #5 $99.67   4.134%   $103.7904   $103.79   $103.80   $103.80  
  Purchase #6 $192.66   4.127%   $200.6111   $200.61   $200.60   $200.60  
  Purchase #7 $197.34   8.698%   $214.5046   $214.50   $214.50   $214.50  
  7 purchase totals = $938.97       $1,004.4214   $1,004.42   $1,004.45   $1,004.50