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	$157.87	6.756%	$168.5357	$168.54	$168.55	$168.50
Purchase #2	$108.80	5.347%	$114.6175	$114.62	$114.60	$114.60
Purchase #3	$40.79	4.301%	$42.5444	$42.54	$42.55	$42.50
Purchase #4	$88.63	9.611%	$97.1482	$97.15	$97.15	$97.10
Purchase #5	$149.67	7.824%	$161.3802	$161.38	$161.40	$161.40
Purchase #6	$90.33	10.650%	$99.9501	$99.95	$99.95	$100.00
Purchase #7	$197.76	7.873%	$213.3296	$213.33	$213.35	$213.30
7 purchase totals =	$833.85		$897.5057	$897.51	$897.55	$897.40