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	$47.39	7.709%	$51.0433	$51.04	$51.05	$51.00
Purchase #2	$82.88	7.774%	$89.3231	$89.32	$89.30	$89.30
Purchase #3	$139.42	6.678%	$148.7305	$148.73	$148.75	$148.70
Purchase #4	$71.54	9.260%	$78.1646	$78.16	$78.15	$78.20
Purchase #5	$224.44	11.472%	$250.1878	$250.19	$250.20	$250.20
Purchase #6	$105.53	6.848%	$112.7567	$112.76	$112.75	$112.80
Purchase #7	$222.72	7.636%	$239.7269	$239.73	$239.75	$239.70
7 purchase totals =	$893.92		$969.9329	$969.93	$969.95	$969.90