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	$155.86	6.196%	$165.5171	$165.52	$165.50	$165.50
Purchase #2	$131.39	13.199%	$148.7322	$148.73	$148.75	$148.70
Purchase #3	$150.78	13.755%	$171.5198	$171.52	$171.50	$171.50
Purchase #4	$20.72	6.854%	$22.1401	$22.14	$22.15	$22.10
Purchase #5	$142.89	7.348%	$153.3896	$153.39	$153.40	$153.40
Purchase #6	$5.46	5.240%	$5.7461	$5.75	$5.75	$5.70
Purchase #7	$234.42	7.127%	$251.1271	$251.13	$251.15	$251.10
7 purchase totals =	$841.52		$918.1720	$918.18	$918.20	$918.00