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	$217.30	6.521%	$231.4701	$231.47	$231.45	$231.50
Purchase #2	$229.54	9.117%	$250.4672	$250.47	$250.45	$250.50
Purchase #3	$107.58	5.702%	$113.7142	$113.71	$113.70	$113.70
Purchase #4	$72.44	7.543%	$77.9041	$77.90	$77.90	$77.90
Purchase #5	$51.88	7.614%	$55.8301	$55.83	$55.85	$55.80
Purchase #6	$204.72	9.328%	$223.8163	$223.82	$223.80	$223.80
Purchase #7	$74.78	3.119%	$77.1124	$77.11	$77.10	$77.10
7 purchase totals =	$958.24		$1,030.3144	$1,030.31	$1,030.25	$1,030.30