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	$25.71	11.567%	$28.6839	$28.68	$28.70	$28.70
Purchase #2	$50.79	11.519%	$56.6405	$56.64	$56.65	$56.60
Purchase #3	$238.48	4.690%	$249.6647	$249.66	$249.65	$249.70
Purchase #4	$179.95	9.698%	$197.4016	$197.40	$197.40	$197.40
Purchase #5	$85.29	6.312%	$90.6735	$90.67	$90.65	$90.70
Purchase #6	$212.47	13.846%	$241.8886	$241.89	$241.90	$241.90
Purchase #7	$52.65	13.734%	$59.881	$59.88	$59.90	$59.90
7 purchase totals =	$845.34		$924.8338	$924.82	$924.85	$924.90