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	$144.66	12.469%	$162.6977	$162.70	$162.70	$162.70
Purchase #2	$190.82	3.102%	$196.7392	$196.74	$196.75	$196.70
Purchase #3	$98.59	6.370%	$104.8702	$104.87	$104.85	$104.90
Purchase #4	$140.96	6.873%	$150.6482	$150.65	$150.65	$150.60
Purchase #5	$148.50	13.170%	$168.0575	$168.06	$168.05	$168.10
Purchase #6	$6.30	8.779%	$6.8531	$6.85	$6.85	$6.90
Purchase #7	$29.82	5.681%	$31.5141	$31.51	$31.50	$31.50
7 purchase totals =	$759.65		$821.3800	$821.38	$821.35	$821.40