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	$139.45	4.195%	$145.2999	$145.30	$145.30	$145.30
Purchase #2	$73.66	12.547%	$82.9021	$82.90	$82.90	$82.90
Purchase #3	$107.92	8.700%	$117.309	$117.31	$117.30	$117.30
Purchase #4	$73.30	7.647%	$78.9053	$78.91	$78.90	$78.90
Purchase #5	$114.84	7.158%	$123.0602	$123.06	$123.05	$123.10
Purchase #6	$70.54	6.264%	$74.9586	$74.96	$74.95	$75.00
Purchase #7	$111.66	12.215%	$125.2993	$125.30	$125.30	$125.30
7 purchase totals =	$691.37		$747.7344	$747.74	$747.70	$747.80