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	$7.78	4.609%	$8.1386	$8.14	$8.15	$8.10
Purchase #2	$159.87	9.387%	$174.877	$174.88	$174.90	$174.90
Purchase #3	$28.86	10.646%	$31.9324	$31.93	$31.95	$31.90
Purchase #4	$92.60	13.533%	$105.1316	$105.13	$105.15	$105.10
Purchase #5	$194.93	5.224%	$205.1131	$205.11	$205.10	$205.10
Purchase #6	$224.87	12.788%	$253.6264	$253.63	$253.65	$253.60
Purchase #7	$199.32	11.629%	$222.4989	$222.50	$222.50	$222.50
7 purchase totals =	$908.23		$1,001.3180	$1,001.32	$1,001.40	$1,001.20