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	$170.90	12.276%	$191.8797	$191.88	$191.90	$191.90
Purchase #2	$65.55	7.486%	$70.4571	$70.46	$70.45	$70.50
Purchase #3	$129.65	12.411%	$145.7409	$145.74	$145.75	$145.70
Purchase #4	$86.40	4.536%	$90.3191	$90.32	$90.30	$90.30
Purchase #5	$246.33	12.854%	$277.9933	$277.99	$278.00	$278.00
Purchase #6	$49.32	13.873%	$56.1622	$56.16	$56.15	$56.20
Purchase #7	$158.81	10.141%	$174.9149	$174.91	$174.90	$174.90
7 purchase totals =	$906.96		$1,007.4672	$1,007.46	$1,007.45	$1,007.50