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	$215.55	3.870%	$223.8918	$223.89	$223.90	$223.90
Purchase #2	$139.34	10.253%	$153.6265	$153.63	$153.65	$153.60
Purchase #3	$53.52	10.702%	$59.2477	$59.25	$59.25	$59.20
Purchase #4	$33.67	3.349%	$34.7976	$34.80	$34.80	$34.80
Purchase #5	$100.54	12.563%	$113.1708	$113.17	$113.15	$113.20
Purchase #6	$234.85	12.416%	$264.009	$264.01	$264.00	$264.00
Purchase #7	$138.76	6.638%	$147.9709	$147.97	$147.95	$148.00
7 purchase totals =	$916.23		$996.7143	$996.72	$996.70	$996.70