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	$12.69	6.391%	$13.501	$13.50	$13.50	$13.50
Purchase #2	$93.43	5.145%	$98.237	$98.24	$98.25	$98.20
Purchase #3	$30.45	11.214%	$33.8647	$33.86	$33.85	$33.90
Purchase #4	$245.32	8.374%	$265.8631	$265.86	$265.85	$265.90
Purchase #5	$19.73	8.282%	$21.364	$21.36	$21.35	$21.40
Purchase #6	$101.58	10.747%	$112.4968	$112.50	$112.50	$112.50
Purchase #7	$123.63	5.206%	$130.0662	$130.07	$130.05	$130.10
7 purchase totals =	$626.83		$675.3928	$675.39	$675.35	$675.50