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	$22.81	4.533%	$23.844	$23.84	$23.85	$23.80
Purchase #2	$215.52	3.869%	$223.8585	$223.86	$223.85	$223.90
Purchase #3	$202.79	4.306%	$211.5221	$211.52	$211.50	$211.50
Purchase #4	$143.56	4.500%	$150.0202	$150.02	$150.00	$150.00
Purchase #5	$90.63	9.392%	$99.142	$99.14	$99.15	$99.10
Purchase #6	$10.52	8.718%	$11.4371	$11.44	$11.45	$11.40
Purchase #7	$62.64	12.524%	$70.485	$70.49	$70.50	$70.50
7 purchase totals =	$748.47		$790.3089	$790.31	$790.30	$790.20