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	$112.48	6.742%	$120.0634	$120.06	$120.05	$120.10
Purchase #2	$183.91	11.123%	$204.3663	$204.37	$204.35	$204.40
Purchase #3	$135.39	6.116%	$143.6705	$143.67	$143.65	$143.70
Purchase #4	$51.49	5.420%	$54.2808	$54.28	$54.30	$54.30
Purchase #5	$128.55	8.444%	$139.4048	$139.40	$139.40	$139.40
Purchase #6	$73.61	6.497%	$78.3924	$78.39	$78.40	$78.40
Purchase #7	$217.88	11.742%	$243.4635	$243.46	$243.45	$243.50
7 purchase totals =	$903.31		$983.6417	$983.63	$983.60	$983.80