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	$145.51	13.594%	$165.2906	$165.29	$165.30	$165.30
Purchase #2	$66.34	9.598%	$72.7073	$72.71	$72.70	$72.70
Purchase #3	$115.54	13.401%	$131.0235	$131.02	$131.00	$131.00
Purchase #4	$73.77	11.654%	$82.3672	$82.37	$82.35	$82.40
Purchase #5	$237.33	7.389%	$254.8663	$254.87	$254.85	$254.90
Purchase #6	$89.85	11.475%	$100.1603	$100.16	$100.15	$100.20
Purchase #7	$38.73	7.297%	$41.5561	$41.56	$41.55	$41.60
7 purchase totals =	$767.07		$847.9713	$847.98	$847.90	$848.10