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	$139.95	7.575%	$150.5512	$150.55	$150.55	$150.60
Purchase #2	$36.52	9.590%	$40.0223	$40.02	$40.00	$40.00
Purchase #3	$156.48	6.274%	$166.2976	$166.30	$166.30	$166.30
Purchase #4	$19.60	4.128%	$20.4091	$20.41	$20.40	$20.40
Purchase #5	$199.55	3.418%	$206.3706	$206.37	$206.35	$206.40
Purchase #6	$94.36	5.563%	$99.6092	$99.61	$99.60	$99.60
Purchase #7	$227.78	5.470%	$240.2396	$240.24	$240.25	$240.20
7 purchase totals =	$874.24		$923.4996	$923.50	$923.45	$923.50