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	$33.82	9.852%	$37.1519	$37.15	$37.15	$37.20
Purchase #2	$108.55	8.152%	$117.399	$117.40	$117.40	$117.40
Purchase #3	$139.74	12.735%	$157.5359	$157.54	$157.55	$157.50
Purchase #4	$49.54	7.507%	$53.259	$53.26	$53.25	$53.30
Purchase #5	$139.40	12.489%	$156.8097	$156.81	$156.80	$156.80
Purchase #6	$187.59	6.736%	$200.2261	$200.23	$200.25	$200.20
Purchase #7	$70.50	9.309%	$77.0628	$77.06	$77.05	$77.10
7 purchase totals =	$729.14		$799.4444	$799.45	$799.45	$799.50