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	$123.93	3.265%	$127.9763	$127.98	$128.00	$128.00
Purchase #2	$39.54	9.846%	$43.4331	$43.43	$43.45	$43.40
Purchase #3	$131.39	12.265%	$147.505	$147.51	$147.50	$147.50
Purchase #4	$154.92	3.110%	$159.738	$159.74	$159.75	$159.70
Purchase #5	$67.59	8.862%	$73.5798	$73.58	$73.60	$73.60
Purchase #6	$213.59	7.562%	$229.7417	$229.74	$229.75	$229.70
Purchase #7	$99.89	4.326%	$104.2112	$104.21	$104.20	$104.20
7 purchase totals =	$830.85		$886.1851	$886.19	$886.25	$886.10