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	$28.82	8.590%	$31.2956	$31.30	$31.30	$31.30
Purchase #2	$32.91	4.820%	$34.4963	$34.50	$34.50	$34.50
Purchase #3	$171.65	10.614%	$189.8689	$189.87	$189.85	$189.90
Purchase #4	$246.55	7.675%	$265.4727	$265.47	$265.45	$265.50
Purchase #5	$94.41	12.138%	$105.8695	$105.87	$105.85	$105.90
Purchase #6	$42.58	12.459%	$47.885	$47.89	$47.90	$47.90
Purchase #7	$110.60	10.329%	$122.0239	$122.02	$122.00	$122.00
7 purchase totals =	$727.52		$796.9119	$796.92	$796.85	$797.00