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	$65.89	13.856%	$75.0197	$75.02	$75.00	$75.00
Purchase #2	$102.93	8.587%	$111.7686	$111.77	$111.75	$111.80
Purchase #3	$220.81	10.305%	$243.5645	$243.56	$243.55	$243.60
Purchase #4	$239.98	4.198%	$250.0544	$250.05	$250.05	$250.10
Purchase #5	$128.39	10.107%	$141.3664	$141.37	$141.35	$141.40
Purchase #6	$107.67	10.185%	$118.6362	$118.64	$118.65	$118.60
Purchase #7	$119.94	4.623%	$125.4848	$125.48	$125.50	$125.50
7 purchase totals =	$985.61		$1,065.8946	$1,065.89	$1,065.85	$1,066.00