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	$37.65	4.786%	$39.4519	$39.45	$39.45	$39.50
Purchase #2	$226.86	9.239%	$247.8196	$247.82	$247.80	$247.80
Purchase #3	$173.84	9.454%	$190.2748	$190.27	$190.25	$190.30
Purchase #4	$63.88	13.386%	$72.431	$72.43	$72.45	$72.40
Purchase #5	$94.35	3.316%	$97.4786	$97.48	$97.50	$97.50
Purchase #6	$103.87	8.107%	$112.2907	$112.29	$112.30	$112.30
Purchase #7	$165.27	10.740%	$183.02	$183.02	$183.00	$183.00
7 purchase totals =	$865.72		$942.7666	$942.76	$942.75	$942.80