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	$154.97	6.498%	$165.04	$165.04	$165.05	$165.00
Purchase #2	$80.75	3.283%	$83.401	$83.40	$83.40	$83.40
Purchase #3	$100.55	3.326%	$103.8943	$103.89	$103.90	$103.90
Purchase #4	$217.39	4.502%	$227.1769	$227.18	$227.20	$227.20
Purchase #5	$135.89	13.681%	$154.4811	$154.48	$154.50	$154.50
Purchase #6	$55.51	5.134%	$58.3599	$58.36	$58.35	$58.40
Purchase #7	$55.42	13.451%	$62.8745	$62.87	$62.85	$62.90
7 purchase totals =	$800.48		$855.2277	$855.22	$855.25	$855.30