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	$167.98	9.720%	$184.3077	$184.31	$184.30	$184.30
Purchase #2	$198.29	12.620%	$223.3142	$223.31	$223.30	$223.30
Purchase #3	$153.95	10.294%	$169.7976	$169.80	$169.80	$169.80
Purchase #4	$19.88	3.654%	$20.6064	$20.61	$20.60	$20.60
Purchase #5	$91.72	10.623%	$101.4634	$101.46	$101.45	$101.50
Purchase #6	$89.57	12.636%	$100.8881	$100.89	$100.90	$100.90
Purchase #7	$129.82	12.820%	$146.4629	$146.46	$146.45	$146.50
7 purchase totals =	$851.21		$946.8403	$946.84	$946.80	$946.90