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	$49.64	9.393%	$54.3027	$54.30	$54.30	$54.30
Purchase #2	$58.40	13.541%	$66.3079	$66.31	$66.30	$66.30
Purchase #3	$129.91	5.368%	$136.8836	$136.88	$136.90	$136.90
Purchase #4	$48.26	9.596%	$52.891	$52.89	$52.90	$52.90
Purchase #5	$127.66	10.615%	$141.2111	$141.21	$141.20	$141.20
Purchase #6	$7.85	13.471%	$8.9075	$8.91	$8.90	$8.90
Purchase #7	$35.96	4.583%	$37.608	$37.61	$37.60	$37.60
7 purchase totals =	$457.68		$498.1118	$498.11	$498.10	$498.10