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	$98.85	11.780%	$110.4945	$110.49	$110.50	$110.50
Purchase #2	$48.91	8.584%	$53.1084	$53.11	$53.10	$53.10
Purchase #3	$92.88	11.424%	$103.4906	$103.49	$103.50	$103.50
Purchase #4	$58.83	8.662%	$63.9259	$63.93	$63.95	$63.90
Purchase #5	$91.25	12.226%	$102.4062	$102.41	$102.40	$102.40
Purchase #6	$127.93	6.390%	$136.1047	$136.10	$136.10	$136.10
Purchase #7	$63.41	12.793%	$71.522	$71.52	$71.50	$71.50
7 purchase totals =	$582.06		$641.0523	$641.05	$641.05	$641.00