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	$86.69	3.209%	$89.4719	$89.47	$89.45	$89.50
Purchase #2	$187.34	12.660%	$211.0572	$211.06	$211.05	$211.10
Purchase #3	$247.73	12.149%	$277.8267	$277.83	$277.85	$277.80
Purchase #4	$121.29	6.459%	$129.1241	$129.12	$129.10	$129.10
Purchase #5	$16.36	11.717%	$18.2769	$18.28	$18.30	$18.30
Purchase #6	$202.58	9.540%	$221.9061	$221.91	$221.90	$221.90
Purchase #7	$173.89	6.546%	$185.2728	$185.27	$185.25	$185.30
7 purchase totals =	$1,035.88		$1,132.9357	$1,132.94	$1,132.90	$1,133.00