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	$167.87	6.332%	$178.4995	$178.50	$178.50	$178.50
Purchase #2	$144.99	7.807%	$156.3094	$156.31	$156.30	$156.30
Purchase #3	$136.91	6.143%	$145.3204	$145.32	$145.30	$145.30
Purchase #4	$91.85	9.410%	$100.4931	$100.49	$100.50	$100.50
Purchase #5	$183.34	3.107%	$189.0364	$189.04	$189.05	$189.00
Purchase #6	$40.75	10.273%	$44.9362	$44.94	$44.95	$44.90
Purchase #7	$89.60	10.830%	$99.3037	$99.30	$99.30	$99.30
7 purchase totals =	$855.31		$913.8987	$913.90	$913.90	$913.80