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	$49.99	6.434%	$53.2064	$53.21	$53.20	$53.20
Purchase #2	$206.33	5.221%	$217.1025	$217.10	$217.10	$217.10
Purchase #3	$214.92	9.756%	$235.8876	$235.89	$235.90	$235.90
Purchase #4	$116.73	5.740%	$123.4303	$123.43	$123.45	$123.40
Purchase #5	$75.33	11.396%	$83.9146	$83.91	$83.90	$83.90
Purchase #6	$112.66	13.163%	$127.4894	$127.49	$127.50	$127.50
Purchase #7	$199.61	5.165%	$209.9199	$209.92	$209.90	$209.90
7 purchase totals =	$975.57		$1,050.9507	$1,050.95	$1,050.95	$1,050.90