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	$38.46	10.275%	$42.4118	$42.41	$42.40	$42.40
Purchase #2	$44.58	8.874%	$48.536	$48.54	$48.55	$48.50
Purchase #3	$38.92	3.559%	$40.3052	$40.31	$40.30	$40.30
Purchase #4	$123.52	13.851%	$140.6288	$140.63	$140.65	$140.60
Purchase #5	$167.50	12.747%	$188.8512	$188.85	$188.85	$188.90
Purchase #6	$35.46	12.548%	$39.9095	$39.91	$39.90	$39.90
Purchase #7	$86.65	5.576%	$91.4816	$91.48	$91.50	$91.50
7 purchase totals =	$535.09		$592.1241	$592.13	$592.15	$592.10