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	$108.79	7.687%	$117.1527	$117.15	$117.15	$117.20
Purchase #2	$160.25	9.730%	$175.8423	$175.84	$175.85	$175.80
Purchase #3	$225.30	12.427%	$253.298	$253.30	$253.30	$253.30
Purchase #4	$109.41	3.543%	$113.2864	$113.29	$113.30	$113.30
Purchase #5	$89.63	3.402%	$92.6792	$92.68	$92.70	$92.70
Purchase #6	$111.39	6.217%	$118.3151	$118.32	$118.30	$118.30
Purchase #7	$188.73	11.738%	$210.8831	$210.88	$210.90	$210.90
7 purchase totals =	$993.50		$1,081.4568	$1,081.46	$1,081.50	$1,081.50