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	$227.91	11.825%	$254.8604	$254.86	$254.85	$254.90
Purchase #2	$15.94	10.198%	$17.5656	$17.57	$17.55	$17.60
Purchase #3	$125.54	13.240%	$142.1615	$142.16	$142.15	$142.20
Purchase #4	$20.61	12.284%	$23.1417	$23.14	$23.15	$23.10
Purchase #5	$183.84	6.681%	$196.1224	$196.12	$196.10	$196.10
Purchase #6	$40.43	4.265%	$42.1543	$42.15	$42.15	$42.20
Purchase #7	$236.45	10.457%	$261.1756	$261.18	$261.20	$261.20
7 purchase totals =	$850.72		$937.1815	$937.18	$937.15	$937.30