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	$73.63	8.738%	$80.0638	$80.06	$80.05	$80.10
Purchase #2	$117.44	5.462%	$123.8546	$123.85	$123.85	$123.90
Purchase #3	$106.54	3.136%	$109.8811	$109.88	$109.90	$109.90
Purchase #4	$193.94	5.314%	$204.246	$204.25	$204.25	$204.20
Purchase #5	$79.44	4.437%	$82.9648	$82.96	$82.95	$83.00
Purchase #6	$179.41	3.762%	$186.1594	$186.16	$186.15	$186.20
Purchase #7	$100.66	4.387%	$105.076	$105.08	$105.10	$105.10
7 purchase totals =	$851.06		$892.2457	$892.24	$892.25	$892.40