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	$239.56	6.689%	$255.5842	$255.58	$255.60	$255.60
Purchase #2	$151.99	12.418%	$170.8641	$170.86	$170.85	$170.90
Purchase #3	$239.86	10.320%	$264.6136	$264.61	$264.60	$264.60
Purchase #4	$33.96	3.591%	$35.1795	$35.18	$35.20	$35.20
Purchase #5	$90.55	5.362%	$95.4053	$95.41	$95.40	$95.40
Purchase #6	$59.48	12.712%	$67.0411	$67.04	$67.05	$67.00
Purchase #7	$126.64	6.429%	$134.7817	$134.78	$134.80	$134.80
7 purchase totals =	$942.04		$1,023.4695	$1,023.46	$1,023.50	$1,023.50