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	$242.59	11.611%	$270.7571	$270.76	$270.75	$270.80
Purchase #2	$82.46	11.470%	$91.9182	$91.92	$91.90	$91.90
Purchase #3	$66.30	3.322%	$68.5025	$68.50	$68.50	$68.50
Purchase #4	$172.30	11.678%	$192.4212	$192.42	$192.40	$192.40
Purchase #5	$250.95	5.362%	$264.4059	$264.41	$264.40	$264.40
Purchase #6	$152.89	9.334%	$167.1608	$167.16	$167.15	$167.20
Purchase #7	$127.77	13.210%	$144.6484	$144.65	$144.65	$144.60
7 purchase totals =	$1,095.26		$1,199.8141	$1,199.82	$1,199.75	$1,199.80