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	$173.35	6.862%	$185.2453	$185.25	$185.25	$185.20
Purchase #2	$238.33	12.653%	$268.4859	$268.49	$268.50	$268.50
Purchase #3	$234.55	10.371%	$258.8752	$258.88	$258.90	$258.90
Purchase #4	$242.42	11.282%	$269.7698	$269.77	$269.75	$269.80
Purchase #5	$240.52	9.560%	$263.5137	$263.51	$263.50	$263.50
Purchase #6	$201.89	13.823%	$229.7973	$229.80	$229.80	$229.80
Purchase #7	$124.76	11.809%	$139.4929	$139.49	$139.50	$139.50
7 purchase totals =	$1,455.82		$1,615.1801	$1,615.19	$1,615.20	$1,615.20