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	$79.79	12.165%	$89.4965	$89.50	$89.50	$89.50
Purchase #2	$110.92	7.397%	$119.1248	$119.12	$119.10	$119.10
Purchase #3	$33.85	7.664%	$36.4443	$36.44	$36.45	$36.40
Purchase #4	$26.72	4.868%	$28.0207	$28.02	$28.00	$28.00
Purchase #5	$188.94	3.856%	$196.2255	$196.23	$196.25	$196.20
Purchase #6	$160.84	9.167%	$175.5842	$175.58	$175.60	$175.60
Purchase #7	$175.37	8.317%	$189.9555	$189.96	$189.95	$190.00
7 purchase totals =	$776.43		$834.8515	$834.85	$834.85	$834.80