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	$247.82	13.614%	$281.5582	$281.56	$281.55	$281.60
Purchase #2	$172.75	12.259%	$193.9274	$193.93	$193.95	$193.90
Purchase #3	$99.55	9.407%	$108.9147	$108.91	$108.90	$108.90
Purchase #4	$79.28	7.698%	$85.383	$85.38	$85.40	$85.40
Purchase #5	$75.65	13.506%	$85.8673	$85.87	$85.85	$85.90
Purchase #6	$53.92	12.655%	$60.7436	$60.74	$60.75	$60.70
Purchase #7	$47.88	12.542%	$53.8851	$53.89	$53.90	$53.90
7 purchase totals =	$776.85		$870.2793	$870.28	$870.30	$870.30