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 $32.86   10.271%   $36.2351   $36.24   $36.25   $36.20  
  Purchase #2 $126.27   4.280%   $131.6744   $131.67   $131.65   $131.70  
  Purchase #3 $241.35   11.230%   $268.4536   $268.45   $268.45   $268.50  
  Purchase #4 $168.36   4.545%   $176.012   $176.01   $176.00   $176.00  
  Purchase #5 $63.30   9.115%   $69.0698   $69.07   $69.05   $69.10  
  Purchase #6 $11.57   4.612%   $12.1036   $12.10   $12.10   $12.10  
  Purchase #7 $6.83   5.116%   $7.1794   $7.18   $7.20   $7.20  
  7 purchase totals = $650.54       $700.7279   $700.72   $700.70   $700.80