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	$91.54	8.468%	$99.2916	$99.29	$99.30	$99.30
Purchase #2	$10.62	12.533%	$11.951	$11.95	$11.95	$12.00
Purchase #3	$53.83	11.193%	$59.8552	$59.86	$59.85	$59.90
Purchase #4	$57.50	7.154%	$61.6136	$61.61	$61.60	$61.60
Purchase #5	$114.40	8.658%	$124.3048	$124.30	$124.30	$124.30
Purchase #6	$100.94	12.817%	$113.8775	$113.88	$113.90	$113.90
Purchase #7	$127.39	9.741%	$139.7991	$139.80	$139.80	$139.80
7 purchase totals =	$556.22		$610.6928	$610.69	$610.70	$610.80