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	$243.54	6.168%	$258.5615	$258.56	$258.55	$258.60
Purchase #2	$62.55	13.179%	$70.7935	$70.79	$70.80	$70.80
Purchase #3	$50.60	3.524%	$52.3831	$52.38	$52.40	$52.40
Purchase #4	$103.48	5.463%	$109.1331	$109.13	$109.15	$109.10
Purchase #5	$25.28	6.419%	$26.9027	$26.90	$26.90	$26.90
Purchase #6	$210.77	9.159%	$230.0744	$230.07	$230.05	$230.10
Purchase #7	$102.61	9.713%	$112.5765	$112.58	$112.60	$112.60
7 purchase totals =	$798.83		$860.4248	$860.41	$860.45	$860.50