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	$137.69	13.750%	$156.6224	$156.62	$156.60	$156.60
Purchase #2	$225.71	10.867%	$250.2379	$250.24	$250.25	$250.20
Purchase #3	$184.87	9.298%	$202.0592	$202.06	$202.05	$202.10
Purchase #4	$37.83	11.749%	$42.2746	$42.27	$42.25	$42.30
Purchase #5	$221.86	10.714%	$245.6301	$245.63	$245.65	$245.60
Purchase #6	$167.62	11.504%	$186.903	$186.90	$186.90	$186.90
Purchase #7	$210.50	6.179%	$223.5068	$223.51	$223.50	$223.50
7 purchase totals =	$1,186.08		$1,307.2340	$1,307.23	$1,307.20	$1,307.20