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	$82.89	8.800%	$90.1843	$90.18	$90.20	$90.20
Purchase #2	$169.84	5.607%	$179.3629	$179.36	$179.35	$179.40
Purchase #3	$124.60	9.245%	$136.1193	$136.12	$136.10	$136.10
Purchase #4	$56.65	9.546%	$62.0578	$62.06	$62.05	$62.10
Purchase #5	$203.74	8.773%	$221.6141	$221.61	$221.60	$221.60
Purchase #6	$78.44	13.765%	$89.2373	$89.24	$89.25	$89.20
Purchase #7	$43.50	10.486%	$48.0614	$48.06	$48.05	$48.10
7 purchase totals =	$759.66		$826.6371	$826.63	$826.60	$826.70