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	$37.30	8.511%	$40.4746	$40.47	$40.45	$40.50
Purchase #2	$217.38	5.571%	$229.4902	$229.49	$229.50	$229.50
Purchase #3	$57.77	12.301%	$64.8763	$64.88	$64.90	$64.90
Purchase #4	$65.40	9.278%	$71.4678	$71.47	$71.45	$71.50
Purchase #5	$45.41	11.631%	$50.6916	$50.69	$50.70	$50.70
Purchase #6	$110.26	11.648%	$123.1031	$123.10	$123.10	$123.10
Purchase #7	$167.35	7.389%	$179.7155	$179.72	$179.70	$179.70
7 purchase totals =	$700.87		$759.8191	$759.82	$759.80	$759.90