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	$54.42	10.115%	$59.9246	$59.92	$59.90	$59.90
Purchase #2	$19.39	4.198%	$20.204	$20.20	$20.20	$20.20
Purchase #3	$216.98	4.235%	$226.1691	$226.17	$226.15	$226.20
Purchase #4	$236.62	12.557%	$266.3324	$266.33	$266.35	$266.30
Purchase #5	$46.31	10.718%	$51.2735	$51.27	$51.25	$51.30
Purchase #6	$135.36	9.261%	$147.8957	$147.90	$147.90	$147.90
Purchase #7	$225.39	9.385%	$246.5429	$246.54	$246.55	$246.50
7 purchase totals =	$934.47		$1,018.3422	$1,018.33	$1,018.30	$1,018.30