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	$97.72	4.627%	$102.2415	$102.24	$102.25	$102.20
Purchase #2	$161.34	13.141%	$182.5417	$182.54	$182.55	$182.50
Purchase #3	$91.85	8.482%	$99.6407	$99.64	$99.65	$99.60
Purchase #4	$161.57	13.371%	$183.1735	$183.17	$183.15	$183.20
Purchase #5	$236.34	4.782%	$247.6418	$247.64	$247.65	$247.60
Purchase #6	$148.27	9.423%	$162.2415	$162.24	$162.25	$162.20
Purchase #7	$156.51	10.859%	$173.5054	$173.51	$173.50	$173.50
7 purchase totals =	$1,053.60		$1,150.9861	$1,150.98	$1,151.00	$1,150.80