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	$171.68	11.413%	$191.2738	$191.27	$191.25	$191.30
Purchase #2	$124.80	12.488%	$140.385	$140.39	$140.40	$140.40
Purchase #3	$68.84	6.873%	$73.5714	$73.57	$73.55	$73.60
Purchase #4	$112.40	10.736%	$124.4673	$124.47	$124.45	$124.50
Purchase #5	$143.83	4.326%	$150.0521	$150.05	$150.05	$150.10
Purchase #6	$138.31	4.297%	$144.2532	$144.25	$144.25	$144.30
Purchase #7	$160.52	9.825%	$176.2911	$176.29	$176.30	$176.30
7 purchase totals =	$920.38		$1,000.2939	$1,000.29	$1,000.25	$1,000.50