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	$120.78	5.629%	$127.5787	$127.58	$127.60	$127.60
Purchase #2	$177.97	4.843%	$186.5891	$186.59	$186.60	$186.60
Purchase #3	$18.70	12.614%	$21.0588	$21.06	$21.05	$21.10
Purchase #4	$66.61	3.731%	$69.0952	$69.10	$69.10	$69.10
Purchase #5	$241.75	3.776%	$250.8785	$250.88	$250.90	$250.90
Purchase #6	$202.78	4.149%	$211.1933	$211.19	$211.20	$211.20
Purchase #7	$196.90	13.672%	$223.8202	$223.82	$223.80	$223.80
7 purchase totals =	$1,025.49		$1,090.2138	$1,090.22	$1,090.25	$1,090.30