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	$30.72	9.801%	$33.7309	$33.73	$33.75	$33.70
Purchase #2	$113.98	8.378%	$123.5292	$123.53	$123.55	$123.50
Purchase #3	$124.67	5.246%	$131.2102	$131.21	$131.20	$131.20
Purchase #4	$83.78	5.700%	$88.5555	$88.56	$88.55	$88.60
Purchase #5	$207.29	9.655%	$227.3038	$227.30	$227.30	$227.30
Purchase #6	$188.54	8.609%	$204.7714	$204.77	$204.75	$204.80
Purchase #7	$46.61	10.259%	$51.3917	$51.39	$51.40	$51.40
7 purchase totals =	$795.59		$860.4927	$860.49	$860.50	$860.50