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	$249.60	10.292%	$275.2888	$275.29	$275.30	$275.30
Purchase #2	$93.99	13.406%	$106.5903	$106.59	$106.60	$106.60
Purchase #3	$229.93	13.792%	$261.6419	$261.64	$261.65	$261.60
Purchase #4	$28.34	11.751%	$31.6702	$31.67	$31.65	$31.70
Purchase #5	$101.74	9.574%	$111.4806	$111.48	$111.50	$111.50
Purchase #6	$197.69	11.165%	$219.7621	$219.76	$219.75	$219.80
Purchase #7	$72.34	6.505%	$77.0457	$77.05	$77.05	$77.00
7 purchase totals =	$973.63		$1,083.4796	$1,083.48	$1,083.50	$1,083.50