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	$227.66	12.581%	$256.3019	$256.30	$256.30	$256.30
Purchase #2	$39.80	6.349%	$42.3269	$42.33	$42.35	$42.30
Purchase #3	$172.71	9.326%	$188.8169	$188.82	$188.80	$188.80
Purchase #4	$93.62	12.321%	$105.1549	$105.15	$105.15	$105.20
Purchase #5	$69.46	4.344%	$72.4773	$72.48	$72.50	$72.50
Purchase #6	$220.83	9.378%	$241.5394	$241.54	$241.55	$241.50
Purchase #7	$19.71	4.858%	$20.6675	$20.67	$20.65	$20.70
7 purchase totals =	$843.79		$927.2848	$927.29	$927.30	$927.30