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	$145.39	7.556%	$156.3757	$156.38	$156.40	$156.40
Purchase #2	$29.79	13.668%	$33.8617	$33.86	$33.85	$33.90
Purchase #3	$39.85	9.290%	$43.5521	$43.55	$43.55	$43.60
Purchase #4	$102.52	7.159%	$109.8594	$109.86	$109.85	$109.90
Purchase #5	$52.54	6.674%	$56.0465	$56.05	$56.05	$56.00
Purchase #6	$130.48	5.785%	$138.0283	$138.03	$138.05	$138.00
Purchase #7	$11.59	9.371%	$12.6761	$12.68	$12.70	$12.70
7 purchase totals =	$512.16		$550.3998	$550.41	$550.45	$550.50