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	$40.65	4.599%	$42.5195	$42.52	$42.50	$42.50
Purchase #2	$19.73	3.809%	$20.4815	$20.48	$20.50	$20.50
Purchase #3	$73.51	11.345%	$81.8497	$81.85	$81.85	$81.80
Purchase #4	$149.86	13.142%	$169.5546	$169.55	$169.55	$169.60
Purchase #5	$96.76	7.372%	$103.8931	$103.89	$103.90	$103.90
Purchase #6	$144.79	5.708%	$153.0546	$153.05	$153.05	$153.10
Purchase #7	$237.91	6.140%	$252.5177	$252.52	$252.50	$252.50
7 purchase totals =	$763.21		$823.8707	$823.86	$823.85	$823.90