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	$30.33	13.313%	$34.3678	$34.37	$34.35	$34.40
Purchase #2	$215.77	9.466%	$236.1948	$236.19	$236.20	$236.20
Purchase #3	$30.65	3.861%	$31.8334	$31.83	$31.85	$31.80
Purchase #4	$92.39	9.201%	$100.8908	$100.89	$100.90	$100.90
Purchase #5	$97.83	13.763%	$111.2943	$111.29	$111.30	$111.30
Purchase #6	$171.28	11.824%	$191.5321	$191.53	$191.55	$191.50
Purchase #7	$165.80	8.851%	$180.475	$180.48	$180.50	$180.50
7 purchase totals =	$804.05		$886.5882	$886.58	$886.65	$886.60