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	$9.91	6.239%	$10.5283	$10.53	$10.55	$10.50
Purchase #2	$39.80	13.251%	$45.0739	$45.07	$45.05	$45.10
Purchase #3	$190.33	5.497%	$200.7924	$200.79	$200.80	$200.80
Purchase #4	$183.49	9.284%	$200.5252	$200.53	$200.55	$200.50
Purchase #5	$53.45	12.530%	$60.1473	$60.15	$60.15	$60.10
Purchase #6	$73.45	5.582%	$77.55	$77.55	$77.55	$77.60
Purchase #7	$215.46	6.704%	$229.9044	$229.90	$229.90	$229.90
7 purchase totals =	$765.89		$824.5215	$824.52	$824.55	$824.50