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	$105.89	11.842%	$118.4295	$118.43	$118.45	$118.40
Purchase #2	$103.76	8.785%	$112.8753	$112.88	$112.90	$112.90
Purchase #3	$55.48	9.789%	$60.9109	$60.91	$60.90	$60.90
Purchase #4	$228.81	11.507%	$255.1392	$255.14	$255.15	$255.10
Purchase #5	$64.47	13.124%	$72.931	$72.93	$72.95	$72.90
Purchase #6	$167.79	8.542%	$182.1226	$182.12	$182.10	$182.10
Purchase #7	$40.41	13.475%	$45.8552	$45.86	$45.85	$45.90
7 purchase totals =	$766.61		$848.2637	$848.27	$848.30	$848.20