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	$81.77	10.433%	$90.3011	$90.30	$90.30	$90.30
Purchase #2	$136.58	10.200%	$150.5112	$150.51	$150.50	$150.50
Purchase #3	$233.96	8.697%	$254.3075	$254.31	$254.30	$254.30
Purchase #4	$31.59	6.167%	$33.5382	$33.54	$33.55	$33.50
Purchase #5	$186.78	4.234%	$194.6883	$194.69	$194.70	$194.70
Purchase #6	$117.59	4.269%	$122.6099	$122.61	$122.60	$122.60
Purchase #7	$229.57	10.743%	$254.2327	$254.23	$254.25	$254.20
7 purchase totals =	$1,017.84		$1,100.1889	$1,100.19	$1,100.20	$1,100.10