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	$222.99	9.825%	$244.8988	$244.90	$244.90	$244.90
Purchase #2	$170.55	6.660%	$181.9086	$181.91	$181.90	$181.90
Purchase #3	$142.63	11.766%	$159.4118	$159.41	$159.40	$159.40
Purchase #4	$235.54	5.116%	$247.5902	$247.59	$247.60	$247.60
Purchase #5	$27.85	5.308%	$29.3283	$29.33	$29.35	$29.30
Purchase #6	$81.44	13.709%	$92.6046	$92.60	$92.60	$92.60
Purchase #7	$250.44	6.103%	$265.7244	$265.72	$265.70	$265.70
7 purchase totals =	$1,131.44		$1,221.4667	$1,221.46	$1,221.45	$1,221.40