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	$47.79	4.812%	$50.0897	$50.09	$50.10	$50.10
Purchase #2	$93.63	11.766%	$104.6465	$104.65	$104.65	$104.60
Purchase #3	$41.54	4.327%	$43.3374	$43.34	$43.35	$43.30
Purchase #4	$93.49	10.579%	$103.3803	$103.38	$103.40	$103.40
Purchase #5	$110.57	12.755%	$124.6732	$124.67	$124.65	$124.70
Purchase #6	$61.45	6.612%	$65.5131	$65.51	$65.50	$65.50
Purchase #7	$102.54	3.155%	$105.7751	$105.78	$105.80	$105.80
7 purchase totals =	$551.01		$597.4153	$597.42	$597.45	$597.40