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	$243.30	11.693%	$271.7491	$271.75	$271.75	$271.70
Purchase #2	$45.49	6.499%	$48.4464	$48.45	$48.45	$48.40
Purchase #3	$89.85	7.333%	$96.4387	$96.44	$96.45	$96.40
Purchase #4	$62.51	4.420%	$65.2729	$65.27	$65.25	$65.30
Purchase #5	$118.74	4.836%	$124.4823	$124.48	$124.50	$124.50
Purchase #6	$103.84	5.713%	$109.7724	$109.77	$109.75	$109.80
Purchase #7	$82.57	6.416%	$87.8677	$87.87	$87.85	$87.90
7 purchase totals =	$746.30		$804.0295	$804.03	$804.00	$804.00