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	$243.42	12.629%	$274.1615	$274.16	$274.15	$274.20
Purchase #2	$37.54	7.262%	$40.2662	$40.27	$40.25	$40.30
Purchase #3	$143.71	8.668%	$156.1668	$156.17	$156.15	$156.20
Purchase #4	$206.94	11.727%	$231.2079	$231.21	$231.20	$231.20
Purchase #5	$126.37	4.360%	$131.8797	$131.88	$131.90	$131.90
Purchase #6	$17.31	12.848%	$19.534	$19.53	$19.55	$19.50
Purchase #7	$71.29	5.355%	$75.1076	$75.11	$75.10	$75.10
7 purchase totals =	$846.58		$928.3237	$928.33	$928.30	$928.40