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	$187.81	12.820%	$211.8872	$211.89	$211.90	$211.90
Purchase #2	$36.36	12.141%	$40.7745	$40.77	$40.75	$40.80
Purchase #3	$224.87	9.339%	$245.8706	$245.87	$245.85	$245.90
Purchase #4	$165.46	4.360%	$172.6741	$172.67	$172.65	$172.70
Purchase #5	$32.76	3.428%	$33.883	$33.88	$33.90	$33.90
Purchase #6	$44.47	12.213%	$49.9011	$49.90	$49.90	$49.90
Purchase #7	$43.44	9.265%	$47.4647	$47.46	$47.45	$47.50
7 purchase totals =	$735.17		$802.4552	$802.44	$802.40	$802.60