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	$72.72	7.577%	$78.23	$78.23	$78.25	$78.20
Purchase #2	$228.65	12.662%	$257.6017	$257.60	$257.60	$257.60
Purchase #3	$52.73	9.221%	$57.5922	$57.59	$57.60	$57.60
Purchase #4	$7.33	10.549%	$8.1032	$8.10	$8.10	$8.10
Purchase #5	$185.59	13.597%	$210.8247	$210.82	$210.80	$210.80
Purchase #6	$24.90	13.452%	$28.2495	$28.25	$28.25	$28.20
Purchase #7	$128.75	10.796%	$142.6499	$142.65	$142.65	$142.60
7 purchase totals =	$700.67		$783.2512	$783.24	$783.25	$783.10