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	$216.42	6.221%	$229.8835	$229.88	$229.90	$229.90
Purchase #2	$36.58	3.267%	$37.7751	$37.78	$37.80	$37.80
Purchase #3	$27.83	13.539%	$31.5979	$31.60	$31.60	$31.60
Purchase #4	$89.63	11.361%	$99.8129	$99.81	$99.80	$99.80
Purchase #5	$231.71	4.768%	$242.7579	$242.76	$242.75	$242.80
Purchase #6	$133.63	8.241%	$144.6424	$144.64	$144.65	$144.60
Purchase #7	$72.92	6.761%	$77.8501	$77.85	$77.85	$77.90
7 purchase totals =	$808.72		$864.3198	$864.32	$864.35	$864.40