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	$187.50	11.220%	$208.5375	$208.54	$208.55	$208.50
Purchase #2	$132.52	8.278%	$143.49	$143.49	$143.50	$143.50
Purchase #3	$184.89	5.702%	$195.4324	$195.43	$195.45	$195.40
Purchase #4	$81.30	5.745%	$85.9707	$85.97	$85.95	$86.00
Purchase #5	$31.56	7.487%	$33.9229	$33.92	$33.90	$33.90
Purchase #6	$81.46	12.808%	$91.8934	$91.89	$91.90	$91.90
Purchase #7	$99.44	10.103%	$109.4864	$109.49	$109.50	$109.50
7 purchase totals =	$798.67		$868.7333	$868.73	$868.75	$868.70