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	$244.25	3.631%	$253.1187	$253.12	$253.10	$253.10
Purchase #2	$134.74	10.691%	$149.1451	$149.15	$149.15	$149.10
Purchase #3	$185.70	7.730%	$200.0546	$200.05	$200.05	$200.10
Purchase #4	$68.96	6.618%	$73.5238	$73.52	$73.50	$73.50
Purchase #5	$52.29	3.293%	$54.0119	$54.01	$54.00	$54.00
Purchase #6	$48.43	10.729%	$53.6261	$53.63	$53.65	$53.60
Purchase #7	$59.54	13.601%	$67.638	$67.64	$67.65	$67.60
7 purchase totals =	$793.91		$851.1182	$851.12	$851.10	$851.00