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	$48.27	9.530%	$52.8701	$52.87	$52.85	$52.90
Purchase #2	$148.69	5.273%	$156.5304	$156.53	$156.55	$156.50
Purchase #3	$225.49	11.297%	$250.9636	$250.96	$250.95	$251.00
Purchase #4	$198.83	9.171%	$217.0647	$217.06	$217.05	$217.10
Purchase #5	$80.56	9.544%	$88.2486	$88.25	$88.25	$88.20
Purchase #6	$51.59	7.544%	$55.4819	$55.48	$55.50	$55.50
Purchase #7	$105.83	11.768%	$118.2841	$118.28	$118.30	$118.30
7 purchase totals =	$859.26		$939.4434	$939.43	$939.45	$939.50