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	$56.73	8.475%	$61.5379	$61.54	$61.55	$61.50
Purchase #2	$231.94	4.390%	$242.1222	$242.12	$242.10	$242.10
Purchase #3	$39.74	7.735%	$42.8139	$42.81	$42.80	$42.80
Purchase #4	$207.41	7.462%	$222.8869	$222.89	$222.90	$222.90
Purchase #5	$7.71	4.291%	$8.0408	$8.04	$8.05	$8.00
Purchase #6	$152.78	12.393%	$171.714	$171.71	$171.70	$171.70
Purchase #7	$171.65	10.221%	$189.1943	$189.19	$189.20	$189.20
7 purchase totals =	$867.96		$938.3100	$938.30	$938.30	$938.20