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	$54.66	3.428%	$56.5337	$56.53	$56.55	$56.50
Purchase #2	$176.74	7.249%	$189.5519	$189.55	$189.55	$189.60
Purchase #3	$91.70	10.314%	$101.1579	$101.16	$101.15	$101.20
Purchase #4	$142.47	4.235%	$148.5036	$148.50	$148.50	$148.50
Purchase #5	$92.90	13.484%	$105.4266	$105.43	$105.45	$105.40
Purchase #6	$202.45	7.399%	$217.4293	$217.43	$217.45	$217.40
Purchase #7	$50.91	11.731%	$56.8823	$56.88	$56.90	$56.90
7 purchase totals =	$811.83		$875.4853	$875.48	$875.55	$875.50