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	$18.39	10.114%	$20.25	$20.25	$20.25	$20.30
Purchase #2	$168.69	7.842%	$181.9187	$181.92	$181.90	$181.90
Purchase #3	$217.32	8.732%	$236.2964	$236.30	$236.30	$236.30
Purchase #4	$154.53	7.214%	$165.6778	$165.68	$165.70	$165.70
Purchase #5	$31.97	4.283%	$33.3393	$33.34	$33.35	$33.30
Purchase #6	$179.64	4.388%	$187.5226	$187.52	$187.50	$187.50
Purchase #7	$238.49	10.495%	$263.5195	$263.52	$263.50	$263.50
7 purchase totals =	$1,009.03		$1,088.5243	$1,088.53	$1,088.50	$1,088.50