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	$40.48	5.627%	$42.7578	$42.76	$42.75	$42.80
Purchase #2	$131.36	12.158%	$147.3307	$147.33	$147.35	$147.30
Purchase #3	$31.57	3.849%	$32.7851	$32.79	$32.80	$32.80
Purchase #4	$192.52	13.858%	$219.1994	$219.20	$219.20	$219.20
Purchase #5	$15.33	12.545%	$17.2531	$17.25	$17.25	$17.30
Purchase #6	$208.31	12.404%	$234.1488	$234.15	$234.15	$234.10
Purchase #7	$135.91	7.179%	$145.667	$145.67	$145.65	$145.70
7 purchase totals =	$755.48		$839.1419	$839.15	$839.15	$839.20