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	$35.73	6.414%	$38.0217	$38.02	$38.00	$38.00
Purchase #2	$226.81	7.855%	$244.6259	$244.63	$244.65	$244.60
Purchase #3	$178.59	6.481%	$190.1644	$190.16	$190.15	$190.20
Purchase #4	$86.27	4.304%	$89.9831	$89.98	$90.00	$90.00
Purchase #5	$120.88	11.503%	$134.7848	$134.78	$134.80	$134.80
Purchase #6	$206.28	5.601%	$217.8337	$217.83	$217.85	$217.80
Purchase #7	$42.89	12.362%	$48.1921	$48.19	$48.20	$48.20
7 purchase totals =	$897.45		$963.6057	$963.59	$963.65	$963.60