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	$144.77	3.819%	$150.2988	$150.30	$150.30	$150.30
Purchase #2	$99.92	5.673%	$105.5885	$105.59	$105.60	$105.60
Purchase #3	$158.79	6.107%	$168.4873	$168.49	$168.50	$168.50
Purchase #4	$225.69	13.524%	$256.2123	$256.21	$256.20	$256.20
Purchase #5	$89.54	4.618%	$93.675	$93.68	$93.70	$93.70
Purchase #6	$9.76	3.151%	$10.0675	$10.07	$10.05	$10.10
Purchase #7	$108.37	13.788%	$123.3121	$123.31	$123.30	$123.30
7 purchase totals =	$836.84		$907.6415	$907.65	$907.65	$907.70