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	$206.46	8.174%	$223.336	$223.34	$223.35	$223.30
Purchase #2	$57.56	13.423%	$65.2863	$65.29	$65.30	$65.30
Purchase #3	$204.93	11.456%	$228.4068	$228.41	$228.40	$228.40
Purchase #4	$185.51	10.765%	$205.4802	$205.48	$205.50	$205.50
Purchase #5	$132.56	13.648%	$150.6518	$150.65	$150.65	$150.70
Purchase #6	$34.50	6.703%	$36.8125	$36.81	$36.80	$36.80
Purchase #7	$29.76	9.713%	$32.6506	$32.65	$32.65	$32.70
7 purchase totals =	$851.28		$942.6242	$942.63	$942.65	$942.70