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	$152.48	8.123%	$164.866	$164.87	$164.85	$164.90
Purchase #2	$229.89	7.366%	$246.8237	$246.82	$246.80	$246.80
Purchase #3	$93.44	6.118%	$99.1567	$99.16	$99.15	$99.20
Purchase #4	$99.85	13.139%	$112.9693	$112.97	$112.95	$113.00
Purchase #5	$219.93	8.464%	$238.5449	$238.54	$238.55	$238.50
Purchase #6	$25.80	3.535%	$26.712	$26.71	$26.70	$26.70
Purchase #7	$71.50	13.862%	$81.4113	$81.41	$81.40	$81.40
7 purchase totals =	$892.89		$970.4839	$970.48	$970.40	$970.50