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	$77.82	3.614%	$80.6324	$80.63	$80.65	$80.60
Purchase #2	$80.96	10.552%	$89.5029	$89.50	$89.50	$89.50
Purchase #3	$29.78	11.663%	$33.2532	$33.25	$33.25	$33.30
Purchase #4	$229.30	3.804%	$238.0226	$238.02	$238.00	$238.00
Purchase #5	$139.27	8.330%	$150.8712	$150.87	$150.85	$150.90
Purchase #6	$150.50	4.509%	$157.286	$157.29	$157.30	$157.30
Purchase #7	$174.49	10.658%	$193.0871	$193.09	$193.10	$193.10
7 purchase totals =	$882.12		$942.6554	$942.65	$942.65	$942.70