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	$242.93	4.382%	$253.5752	$253.58	$253.60	$253.60
Purchase #2	$116.47	10.404%	$128.5875	$128.59	$128.60	$128.60
Purchase #3	$110.91	3.121%	$114.3715	$114.37	$114.35	$114.40
Purchase #4	$110.88	7.221%	$118.8866	$118.89	$118.90	$118.90
Purchase #5	$14.48	10.103%	$15.9429	$15.94	$15.95	$15.90
Purchase #6	$57.30	10.658%	$63.407	$63.41	$63.40	$63.40
Purchase #7	$139.46	8.115%	$150.7772	$150.78	$150.80	$150.80
7 purchase totals =	$792.43		$845.5479	$845.56	$845.60	$845.60