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 $33.88   6.124%   $35.9548   $35.95   $35.95   $36.00  
  Purchase #2 $14.74   8.477%   $15.9895   $15.99   $16.00   $16.00  
  Purchase #3 $57.82   13.753%   $65.772   $65.77   $65.75   $65.80  
  Purchase #4 $176.25   9.395%   $192.8087   $192.81   $192.80   $192.80  
  Purchase #5 $67.39   11.259%   $74.9774   $74.98   $75.00   $75.00  
  Purchase #6 $92.53   9.223%   $101.064   $101.06   $101.05   $101.10  
  Purchase #7 $105.60   12.752%   $119.0661   $119.07   $119.05   $119.10  
  7 purchase totals = $548.21       $605.6325   $605.63   $605.60   $605.80