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	$43.31	13.379%	$49.1044	$49.10	$49.10	$49.10
Purchase #2	$45.61	3.252%	$47.0932	$47.09	$47.10	$47.10
Purchase #3	$139.72	10.459%	$154.3333	$154.33	$154.35	$154.30
Purchase #4	$78.65	8.767%	$85.5452	$85.55	$85.55	$85.50
Purchase #5	$50.63	8.829%	$55.1001	$55.10	$55.10	$55.10
Purchase #6	$206.40	7.704%	$222.3011	$222.30	$222.30	$222.30
Purchase #7	$129.71	6.156%	$137.6949	$137.69	$137.70	$137.70
7 purchase totals =	$694.03		$751.1722	$751.16	$751.20	$751.10