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	$42.53	6.514%	$45.3004	$45.30	$45.30	$45.30
Purchase #2	$152.35	7.827%	$164.2744	$164.27	$164.25	$164.30
Purchase #3	$229.92	6.380%	$244.5889	$244.59	$244.60	$244.60
Purchase #4	$109.87	6.357%	$116.8544	$116.85	$116.85	$116.90
Purchase #5	$178.90	7.602%	$192.5	$192.50	$192.50	$192.50
Purchase #6	$222.65	12.478%	$250.4323	$250.43	$250.45	$250.40
Purchase #7	$68.92	12.297%	$77.3951	$77.40	$77.40	$77.40
7 purchase totals =	$1,005.14		$1,091.3455	$1,091.34	$1,091.35	$1,091.40