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	$54.35	4.547%	$56.8213	$56.82	$56.80	$56.80
Purchase #2	$99.76	6.322%	$106.0668	$106.07	$106.05	$106.10
Purchase #3	$186.25	7.325%	$199.8928	$199.89	$199.90	$199.90
Purchase #4	$229.42	6.578%	$244.5112	$244.51	$244.50	$244.50
Purchase #5	$39.33	9.547%	$43.0848	$43.08	$43.10	$43.10
Purchase #6	$87.46	3.639%	$90.6427	$90.64	$90.65	$90.60
Purchase #7	$40.44	5.802%	$42.7863	$42.79	$42.80	$42.80
7 purchase totals =	$737.01		$783.8059	$783.80	$783.80	$783.80