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	$186.27	9.763%	$204.4555	$204.46	$204.45	$204.50
Purchase #2	$98.67	11.371%	$109.8898	$109.89	$109.90	$109.90
Purchase #3	$171.45	9.840%	$188.3207	$188.32	$188.30	$188.30
Purchase #4	$134.35	8.778%	$146.1432	$146.14	$146.15	$146.10
Purchase #5	$90.68	7.434%	$97.4212	$97.42	$97.40	$97.40
Purchase #6	$105.42	7.319%	$113.1357	$113.14	$113.15	$113.10
Purchase #7	$100.75	10.502%	$111.3308	$111.33	$111.35	$111.30
7 purchase totals =	$887.59		$970.6969	$970.70	$970.70	$970.60