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	$109.83	12.292%	$123.3303	$123.33	$123.35	$123.30
Purchase #2	$136.91	4.141%	$142.5794	$142.58	$142.60	$142.60
Purchase #3	$55.93	5.128%	$58.7981	$58.80	$58.80	$58.80
Purchase #4	$196.57	6.405%	$209.1603	$209.16	$209.15	$209.20
Purchase #5	$101.62	4.208%	$105.8962	$105.90	$105.90	$105.90
Purchase #6	$18.85	6.682%	$20.1096	$20.11	$20.10	$20.10
Purchase #7	$244.95	11.496%	$273.1095	$273.11	$273.10	$273.10
7 purchase totals =	$864.66		$932.9834	$932.99	$933.00	$933.00