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	$235.96	5.565%	$249.0912	$249.09	$249.10	$249.10
Purchase #2	$59.90	12.315%	$67.2767	$67.28	$67.30	$67.30
Purchase #3	$234.39	8.798%	$255.0116	$255.01	$255.00	$255.00
Purchase #4	$40.94	13.256%	$46.367	$46.37	$46.35	$46.40
Purchase #5	$206.31	6.822%	$220.3845	$220.38	$220.40	$220.40
Purchase #6	$171.83	12.199%	$192.7915	$192.79	$192.80	$192.80
Purchase #7	$88.50	11.196%	$98.4085	$98.41	$98.40	$98.40
7 purchase totals =	$1,037.83		$1,129.3310	$1,129.33	$1,129.35	$1,129.40