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	$230.31	3.446%	$238.2465	$238.25	$238.25	$238.20
Purchase #2	$33.71	12.617%	$37.9632	$37.96	$37.95	$38.00
Purchase #3	$202.83	10.220%	$223.5592	$223.56	$223.55	$223.60
Purchase #4	$14.87	11.663%	$16.6043	$16.60	$16.60	$16.60
Purchase #5	$89.40	11.722%	$99.8795	$99.88	$99.90	$99.90
Purchase #6	$30.45	5.870%	$32.2374	$32.24	$32.25	$32.20
Purchase #7	$232.61	7.547%	$250.1651	$250.17	$250.15	$250.20
7 purchase totals =	$834.18		$898.6552	$898.66	$898.65	$898.70