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	$83.89	9.359%	$91.7413	$91.74	$91.75	$91.70
Purchase #2	$140.50	8.839%	$152.9188	$152.92	$152.90	$152.90
Purchase #3	$29.99	9.626%	$32.8768	$32.88	$32.90	$32.90
Purchase #4	$178.62	3.536%	$184.936	$184.94	$184.95	$184.90
Purchase #5	$113.85	12.190%	$127.7283	$127.73	$127.75	$127.70
Purchase #6	$210.47	3.546%	$217.9333	$217.93	$217.95	$217.90
Purchase #7	$72.67	13.152%	$82.2276	$82.23	$82.25	$82.20
7 purchase totals =	$829.99		$890.3621	$890.37	$890.45	$890.20