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	$11.92	5.573%	$12.5843	$12.58	$12.60	$12.60
Purchase #2	$52.51	9.761%	$57.6355	$57.64	$57.65	$57.60
Purchase #3	$219.64	6.199%	$233.2555	$233.26	$233.25	$233.30
Purchase #4	$49.45	7.421%	$53.1197	$53.12	$53.10	$53.10
Purchase #5	$53.53	5.316%	$56.3757	$56.38	$56.40	$56.40
Purchase #6	$126.89	7.503%	$136.4106	$136.41	$136.40	$136.40
Purchase #7	$147.50	9.841%	$162.0155	$162.02	$162.00	$162.00
7 purchase totals =	$661.44		$711.3968	$711.41	$711.40	$711.40