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	$60.28	10.203%	$66.4304	$66.43	$66.45	$66.40
Purchase #2	$180.44	10.387%	$199.1823	$199.18	$199.20	$199.20
Purchase #3	$53.42	12.255%	$59.9666	$59.97	$59.95	$60.00
Purchase #4	$218.87	12.560%	$246.3601	$246.36	$246.35	$246.40
Purchase #5	$168.50	3.735%	$174.7935	$174.79	$174.80	$174.80
Purchase #6	$147.49	13.543%	$167.4646	$167.46	$167.45	$167.50
Purchase #7	$100.33	3.156%	$103.4964	$103.50	$103.50	$103.50
7 purchase totals =	$929.33		$1,017.6939	$1,017.69	$1,017.70	$1,017.80