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	$78.75	7.741%	$84.846	$84.85	$84.85	$84.80
Purchase #2	$78.89	9.647%	$86.5005	$86.50	$86.50	$86.50
Purchase #3	$54.97	8.717%	$59.7617	$59.76	$59.75	$59.80
Purchase #4	$143.40	6.367%	$152.5303	$152.53	$152.55	$152.50
Purchase #5	$196.85	5.202%	$207.0901	$207.09	$207.10	$207.10
Purchase #6	$236.81	9.544%	$259.4111	$259.41	$259.40	$259.40
Purchase #7	$218.88	5.628%	$231.1986	$231.20	$231.20	$231.20
7 purchase totals =	$1,008.55		$1,081.3383	$1,081.34	$1,081.35	$1,081.30