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	$168.72	6.410%	$179.535	$179.54	$179.55	$179.50
Purchase #2	$229.45	9.262%	$250.7017	$250.70	$250.70	$250.70
Purchase #3	$225.26	8.669%	$244.7878	$244.79	$244.80	$244.80
Purchase #4	$54.72	12.262%	$61.4298	$61.43	$61.45	$61.40
Purchase #5	$147.41	12.803%	$166.2829	$166.28	$166.30	$166.30
Purchase #6	$82.29	6.863%	$87.9376	$87.94	$87.95	$87.90
Purchase #7	$244.94	8.200%	$265.0251	$265.03	$265.05	$265.00
7 purchase totals =	$1,152.79		$1,255.6999	$1,255.71	$1,255.80	$1,255.60