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	$175.97	7.144%	$188.5413	$188.54	$188.55	$188.50
Purchase #2	$235.74	8.310%	$255.33	$255.33	$255.35	$255.30
Purchase #3	$192.92	11.590%	$215.2794	$215.28	$215.30	$215.30
Purchase #4	$48.65	6.406%	$51.7665	$51.77	$51.75	$51.80
Purchase #5	$177.55	7.315%	$190.5378	$190.54	$190.55	$190.50
Purchase #6	$148.46	8.151%	$160.561	$160.56	$160.55	$160.60
Purchase #7	$202.66	7.752%	$218.3702	$218.37	$218.35	$218.40
7 purchase totals =	$1,181.95		$1,280.3862	$1,280.39	$1,280.40	$1,280.40