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	$27.48	4.781%	$28.7938	$28.79	$28.80	$28.80
Purchase #2	$92.73	8.804%	$100.8939	$100.89	$100.90	$100.90
Purchase #3	$177.82	3.353%	$183.7823	$183.78	$183.80	$183.80
Purchase #4	$131.66	6.209%	$139.8348	$139.83	$139.85	$139.80
Purchase #5	$147.78	9.667%	$162.0659	$162.07	$162.05	$162.10
Purchase #6	$209.83	11.634%	$234.2416	$234.24	$234.25	$234.20
Purchase #7	$64.88	11.640%	$72.432	$72.43	$72.45	$72.40
7 purchase totals =	$852.18		$922.0443	$922.03	$922.10	$922.00