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	$172.80	5.672%	$182.6012	$182.60	$182.60	$182.60
Purchase #2	$233.64	11.809%	$261.2305	$261.23	$261.25	$261.20
Purchase #3	$124.35	4.511%	$129.9594	$129.96	$129.95	$130.00
Purchase #4	$92.55	8.627%	$100.5343	$100.53	$100.55	$100.50
Purchase #5	$42.31	3.655%	$43.8564	$43.86	$43.85	$43.90
Purchase #6	$40.75	9.627%	$44.673	$44.67	$44.65	$44.70
Purchase #7	$39.77	6.818%	$42.4815	$42.48	$42.50	$42.50
7 purchase totals =	$746.17		$805.3363	$805.33	$805.35	$805.40