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	$124.78	10.459%	$137.8307	$137.83	$137.85	$137.80
Purchase #2	$161.50	3.185%	$166.6438	$166.64	$166.65	$166.60
Purchase #3	$60.31	5.753%	$63.7796	$63.78	$63.80	$63.80
Purchase #4	$53.46	11.634%	$59.6795	$59.68	$59.70	$59.70
Purchase #5	$236.36	13.306%	$267.8101	$267.81	$267.80	$267.80
Purchase #6	$83.80	7.774%	$90.3146	$90.31	$90.30	$90.30
Purchase #7	$126.90	3.624%	$131.4989	$131.50	$131.50	$131.50
7 purchase totals =	$847.11		$917.5572	$917.55	$917.60	$917.50