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	$134.81	7.546%	$144.9828	$144.98	$145.00	$145.00
Purchase #2	$74.61	8.243%	$80.7601	$80.76	$80.75	$80.80
Purchase #3	$185.97	11.152%	$206.7094	$206.71	$206.70	$206.70
Purchase #4	$114.74	7.561%	$123.4155	$123.42	$123.40	$123.40
Purchase #5	$74.63	8.350%	$80.8616	$80.86	$80.85	$80.90
Purchase #6	$130.76	6.671%	$139.483	$139.48	$139.50	$139.50
Purchase #7	$18.32	12.818%	$20.6683	$20.67	$20.65	$20.70
7 purchase totals =	$733.84		$796.8807	$796.88	$796.85	$797.00