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	$142.36	12.329%	$159.9116	$159.91	$159.90	$159.90
Purchase #2	$138.93	8.562%	$150.8252	$150.83	$150.85	$150.80
Purchase #3	$111.74	11.197%	$124.2515	$124.25	$124.25	$124.30
Purchase #4	$223.59	4.336%	$233.2849	$233.28	$233.30	$233.30
Purchase #5	$171.96	4.287%	$179.3319	$179.33	$179.35	$179.30
Purchase #6	$34.31	8.349%	$37.1745	$37.17	$37.15	$37.20
Purchase #7	$227.42	9.453%	$248.918	$248.92	$248.90	$248.90
7 purchase totals =	$1,050.31		$1,133.6976	$1,133.69	$1,133.70	$1,133.70