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	$136.69	13.614%	$155.299	$155.30	$155.30	$155.30
Purchase #2	$30.31	13.829%	$34.5016	$34.50	$34.50	$34.50
Purchase #3	$183.76	13.279%	$208.1615	$208.16	$208.15	$208.20
Purchase #4	$140.40	7.202%	$150.5116	$150.51	$150.50	$150.50
Purchase #5	$83.87	6.413%	$89.2486	$89.25	$89.25	$89.20
Purchase #6	$31.70	11.442%	$35.3271	$35.33	$35.35	$35.30
Purchase #7	$188.66	3.551%	$195.3593	$195.36	$195.35	$195.40
7 purchase totals =	$795.39		$868.4087	$868.41	$868.40	$868.40