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	$165.57	8.157%	$179.0755	$179.08	$179.10	$179.10
Purchase #2	$189.96	4.402%	$198.322	$198.32	$198.30	$198.30
Purchase #3	$78.39	13.241%	$88.7696	$88.77	$88.75	$88.80
Purchase #4	$69.87	6.532%	$74.4339	$74.43	$74.45	$74.40
Purchase #5	$94.35	6.207%	$100.2063	$100.21	$100.20	$100.20
Purchase #6	$137.85	3.671%	$142.9105	$142.91	$142.90	$142.90
Purchase #7	$98.58	6.658%	$105.1435	$105.14	$105.15	$105.10
7 purchase totals =	$834.57		$888.8613	$888.86	$888.85	$888.80