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	$250.28	13.805%	$284.8312	$284.83	$284.85	$284.80
Purchase #2	$187.83	11.290%	$209.036	$209.04	$209.05	$209.00
Purchase #3	$151.72	10.154%	$167.1256	$167.13	$167.15	$167.10
Purchase #4	$30.95	4.869%	$32.457	$32.46	$32.45	$32.50
Purchase #5	$164.65	3.801%	$170.9083	$170.91	$170.90	$170.90
Purchase #6	$75.34	3.677%	$78.1103	$78.11	$78.10	$78.10
Purchase #7	$100.54	7.169%	$107.7477	$107.75	$107.75	$107.70
7 purchase totals =	$961.31		$1,050.2161	$1,050.23	$1,050.25	$1,050.10