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	$123.86	3.370%	$128.0341	$128.03	$128.05	$128.00
Purchase #2	$55.51	12.498%	$62.4476	$62.45	$62.45	$62.40
Purchase #3	$54.50	12.855%	$61.506	$61.51	$61.50	$61.50
Purchase #4	$117.74	5.364%	$124.0556	$124.06	$124.05	$124.10
Purchase #5	$139.36	10.818%	$154.436	$154.44	$154.45	$154.40
Purchase #6	$45.40	11.533%	$50.636	$50.64	$50.65	$50.60
Purchase #7	$47.80	13.394%	$54.2023	$54.20	$54.20	$54.20
7 purchase totals =	$584.17		$635.3176	$635.33	$635.35	$635.20