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	$45.97	10.472%	$50.784	$50.78	$50.80	$50.80
Purchase #2	$84.52	6.351%	$89.8879	$89.89	$89.90	$89.90
Purchase #3	$155.99	11.548%	$174.0037	$174.00	$174.00	$174.00
Purchase #4	$200.44	3.149%	$206.7519	$206.75	$206.75	$206.80
Purchase #5	$171.32	6.501%	$182.4575	$182.46	$182.45	$182.50
Purchase #6	$61.91	3.763%	$64.2397	$64.24	$64.25	$64.20
Purchase #7	$10.73	5.818%	$11.3543	$11.35	$11.35	$11.40
7 purchase totals =	$730.88		$779.4790	$779.47	$779.50	$779.60