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	$39.47	6.775%	$42.1441	$42.14	$42.15	$42.10
Purchase #2	$151.34	12.499%	$170.256	$170.26	$170.25	$170.30
Purchase #3	$182.37	4.303%	$190.2174	$190.22	$190.20	$190.20
Purchase #4	$173.40	12.371%	$194.8513	$194.85	$194.85	$194.90
Purchase #5	$115.30	6.817%	$123.16	$123.16	$123.15	$123.20
Purchase #6	$99.91	10.215%	$110.1158	$110.12	$110.10	$110.10
Purchase #7	$191.89	8.756%	$208.6919	$208.69	$208.70	$208.70
7 purchase totals =	$953.68		$1,039.4365	$1,039.44	$1,039.40	$1,039.50