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	$121.73	11.797%	$136.0905	$136.09	$136.10	$136.10
Purchase #2	$202.50	3.661%	$209.9135	$209.91	$209.90	$209.90
Purchase #3	$29.28	7.535%	$31.4862	$31.49	$31.50	$31.50
Purchase #4	$133.50	9.182%	$145.758	$145.76	$145.75	$145.80
Purchase #5	$188.50	4.425%	$196.8411	$196.84	$196.85	$196.80
Purchase #6	$152.93	4.164%	$159.298	$159.30	$159.30	$159.30
Purchase #7	$30.83	6.761%	$32.9144	$32.91	$32.90	$32.90
7 purchase totals =	$859.27		$912.3017	$912.30	$912.30	$912.30