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	$169.95	6.441%	$180.8965	$180.90	$180.90	$180.90
Purchase #2	$62.54	7.711%	$67.3625	$67.36	$67.35	$67.40
Purchase #3	$106.77	4.119%	$111.1679	$111.17	$111.15	$111.20
Purchase #4	$135.42	6.826%	$144.6638	$144.66	$144.65	$144.70
Purchase #5	$151.88	7.182%	$162.788	$162.79	$162.80	$162.80
Purchase #6	$74.27	11.274%	$82.6432	$82.64	$82.65	$82.60
Purchase #7	$77.72	13.560%	$88.2588	$88.26	$88.25	$88.30
7 purchase totals =	$778.55		$837.7807	$837.78	$837.75	$837.90