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	$87.25	13.637%	$99.1483	$99.15	$99.15	$99.10
Purchase #2	$59.62	10.465%	$65.8592	$65.86	$65.85	$65.90
Purchase #3	$229.35	12.505%	$258.0302	$258.03	$258.05	$258.00
Purchase #4	$98.51	10.682%	$109.0328	$109.03	$109.05	$109.00
Purchase #5	$56.74	12.378%	$63.7633	$63.76	$63.75	$63.80
Purchase #6	$99.65	13.257%	$112.8606	$112.86	$112.85	$112.90
Purchase #7	$88.42	3.521%	$91.5333	$91.53	$91.55	$91.50
7 purchase totals =	$719.54		$800.2277	$800.22	$800.25	$800.20