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	$7.44	4.685%	$7.7886	$7.79	$7.80	$7.80
Purchase #2	$195.76	13.453%	$222.0956	$222.10	$222.10	$222.10
Purchase #3	$164.86	10.520%	$182.2033	$182.20	$182.20	$182.20
Purchase #4	$211.85	4.530%	$221.4468	$221.45	$221.45	$221.40
Purchase #5	$18.85	8.152%	$20.3867	$20.39	$20.40	$20.40
Purchase #6	$10.82	8.137%	$11.7004	$11.70	$11.70	$11.70
Purchase #7	$150.33	6.786%	$160.5314	$160.53	$160.55	$160.50
7 purchase totals =	$759.91		$826.1528	$826.16	$826.20	$826.10