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	$220.79	8.391%	$239.3165	$239.32	$239.30	$239.30
Purchase #2	$33.29	11.440%	$37.0984	$37.10	$37.10	$37.10
Purchase #3	$218.30	12.624%	$245.8582	$245.86	$245.85	$245.90
Purchase #4	$134.48	6.232%	$142.8608	$142.86	$142.85	$142.90
Purchase #5	$103.26	6.438%	$109.9079	$109.91	$109.90	$109.90
Purchase #6	$47.28	3.352%	$48.8648	$48.86	$48.85	$48.90
Purchase #7	$94.50	3.872%	$98.159	$98.16	$98.15	$98.20
7 purchase totals =	$851.90		$922.0656	$922.07	$922.00	$922.20