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	$151.36	13.712%	$172.1145	$172.11	$172.10	$172.10
Purchase #2	$19.55	6.467%	$20.8143	$20.81	$20.80	$20.80
Purchase #3	$55.66	6.559%	$59.3107	$59.31	$59.30	$59.30
Purchase #4	$74.61	11.837%	$83.4416	$83.44	$83.45	$83.40
Purchase #5	$183.81	11.375%	$204.7184	$204.72	$204.70	$204.70
Purchase #6	$31.31	4.802%	$32.8135	$32.81	$32.80	$32.80
Purchase #7	$178.45	4.619%	$186.6926	$186.69	$186.70	$186.70
7 purchase totals =	$694.75		$759.9056	$759.89	$759.85	$759.80