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	$80.49	3.496%	$83.3039	$83.30	$83.30	$83.30
Purchase #2	$141.78	8.141%	$153.3223	$153.32	$153.30	$153.30
Purchase #3	$72.28	9.247%	$78.9637	$78.96	$78.95	$79.00
Purchase #4	$32.42	11.427%	$36.1246	$36.12	$36.10	$36.10
Purchase #5	$166.45	11.629%	$185.8065	$185.81	$185.80	$185.80
Purchase #6	$153.80	8.845%	$167.4036	$167.40	$167.40	$167.40
Purchase #7	$202.35	8.382%	$219.311	$219.31	$219.30	$219.30
7 purchase totals =	$849.57		$924.2356	$924.22	$924.15	$924.20