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	$89.53	9.839%	$98.3389	$98.34	$98.35	$98.30
Purchase #2	$158.66	8.169%	$171.6209	$171.62	$171.60	$171.60
Purchase #3	$6.89	4.177%	$7.1778	$7.18	$7.20	$7.20
Purchase #4	$185.72	4.428%	$193.9437	$193.94	$193.95	$193.90
Purchase #5	$61.64	4.394%	$64.3485	$64.35	$64.35	$64.30
Purchase #6	$222.72	4.542%	$232.8359	$232.84	$232.85	$232.80
Purchase #7	$85.35	5.848%	$90.3413	$90.34	$90.35	$90.30
7 purchase totals =	$810.51		$858.6070	$858.61	$858.65	$858.40