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	$50.47	5.565%	$53.2787	$53.28	$53.30	$53.30
Purchase #2	$246.99	8.463%	$267.8928	$267.89	$267.90	$267.90
Purchase #3	$41.33	10.353%	$45.6089	$45.61	$45.60	$45.60
Purchase #4	$244.49	10.778%	$270.8411	$270.84	$270.85	$270.80
Purchase #5	$232.61	6.123%	$246.8527	$246.85	$246.85	$246.90
Purchase #6	$98.88	13.759%	$112.4849	$112.48	$112.50	$112.50
Purchase #7	$62.76	10.187%	$69.1534	$69.15	$69.15	$69.20
7 purchase totals =	$977.53		$1,066.1125	$1,066.10	$1,066.15	$1,066.20