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	$247.50	8.449%	$268.4113	$268.41	$268.40	$268.40
Purchase #2	$63.59	4.667%	$66.5577	$66.56	$66.55	$66.60
Purchase #3	$196.26	6.858%	$209.7195	$209.72	$209.70	$209.70
Purchase #4	$92.32	7.756%	$99.4803	$99.48	$99.50	$99.50
Purchase #5	$79.93	13.717%	$90.894	$90.89	$90.90	$90.90
Purchase #6	$15.33	4.576%	$16.0315	$16.03	$16.05	$16.00
Purchase #7	$228.78	7.844%	$246.7255	$246.73	$246.75	$246.70
7 purchase totals =	$923.71		$997.8198	$997.82	$997.85	$997.80