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	$240.90	3.826%	$250.1168	$250.12	$250.10	$250.10
Purchase #2	$54.89	13.493%	$62.2963	$62.30	$62.30	$62.30
Purchase #3	$150.25	5.311%	$158.2298	$158.23	$158.25	$158.20
Purchase #4	$126.83	9.338%	$138.6734	$138.67	$138.65	$138.70
Purchase #5	$149.74	4.753%	$156.8571	$156.86	$156.85	$156.90
Purchase #6	$88.53	10.850%	$98.1355	$98.14	$98.15	$98.10
Purchase #7	$166.78	12.848%	$188.2079	$188.21	$188.20	$188.20
7 purchase totals =	$977.92		$1,052.5168	$1,052.53	$1,052.50	$1,052.50