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	$84.37	6.870%	$90.1662	$90.17	$90.15	$90.20
Purchase #2	$236.49	4.822%	$247.8935	$247.89	$247.90	$247.90
Purchase #3	$82.37	7.133%	$88.2455	$88.25	$88.25	$88.20
Purchase #4	$162.52	6.759%	$173.5047	$173.50	$173.50	$173.50
Purchase #5	$52.61	6.481%	$56.0197	$56.02	$56.00	$56.00
Purchase #6	$116.59	5.501%	$123.0036	$123.00	$123.00	$123.00
Purchase #7	$65.36	12.679%	$73.647	$73.65	$73.65	$73.60
7 purchase totals =	$800.31		$852.4802	$852.48	$852.45	$852.40