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	$154.83	3.302%	$159.9425	$159.94	$159.95	$159.90
Purchase #2	$12.33	7.815%	$13.2936	$13.29	$13.30	$13.30
Purchase #3	$46.27	9.151%	$50.5042	$50.50	$50.50	$50.50
Purchase #4	$47.43	5.506%	$50.0415	$50.04	$50.05	$50.00
Purchase #5	$34.53	7.740%	$37.2026	$37.20	$37.20	$37.20
Purchase #6	$112.90	13.315%	$127.9326	$127.93	$127.95	$127.90
Purchase #7	$50.59	11.565%	$56.4407	$56.44	$56.45	$56.40
7 purchase totals =	$458.88		$495.3577	$495.34	$495.40	$495.20