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	$76.35	5.404%	$80.476	$80.48	$80.50	$80.50
Purchase #2	$91.47	3.356%	$94.5397	$94.54	$94.55	$94.50
Purchase #3	$43.55	5.748%	$46.0533	$46.05	$46.05	$46.10
Purchase #4	$167.56	10.607%	$185.3331	$185.33	$185.35	$185.30
Purchase #5	$221.70	5.494%	$233.8802	$233.88	$233.90	$233.90
Purchase #6	$176.71	13.219%	$200.0693	$200.07	$200.05	$200.10
Purchase #7	$18.50	8.385%	$20.0512	$20.05	$20.05	$20.10
7 purchase totals =	$795.84		$860.4028	$860.40	$860.45	$860.50