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	$6.92	8.843%	$7.5319	$7.53	$7.55	$7.50
Purchase #2	$173.46	11.217%	$192.917	$192.92	$192.90	$192.90
Purchase #3	$145.34	11.287%	$161.7445	$161.74	$161.75	$161.70
Purchase #4	$175.42	4.140%	$182.6824	$182.68	$182.70	$182.70
Purchase #5	$89.63	12.593%	$100.9171	$100.92	$100.90	$100.90
Purchase #6	$20.26	6.393%	$21.5552	$21.56	$21.55	$21.60
Purchase #7	$130.56	8.445%	$141.5858	$141.59	$141.60	$141.60
7 purchase totals =	$741.59		$808.9339	$808.94	$808.95	$808.90