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	$142.40	3.389%	$147.2259	$147.23	$147.25	$147.20
Purchase #2	$156.44	6.857%	$167.1671	$167.17	$167.15	$167.20
Purchase #3	$132.61	9.607%	$145.3498	$145.35	$145.35	$145.30
Purchase #4	$123.66	11.175%	$137.479	$137.48	$137.50	$137.50
Purchase #5	$5.93	13.405%	$6.7249	$6.72	$6.70	$6.70
Purchase #6	$165.87	10.531%	$183.3378	$183.34	$183.35	$183.30
Purchase #7	$85.82	3.789%	$89.0717	$89.07	$89.05	$89.10
7 purchase totals =	$812.73		$876.3562	$876.36	$876.35	$876.30