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	$44.38	6.779%	$47.3885	$47.39	$47.40	$47.40
Purchase #2	$234.46	3.415%	$242.4668	$242.47	$242.45	$242.50
Purchase #3	$69.32	13.108%	$78.4065	$78.41	$78.40	$78.40
Purchase #4	$247.83	11.262%	$275.7406	$275.74	$275.75	$275.70
Purchase #5	$20.50	8.227%	$22.1865	$22.19	$22.20	$22.20
Purchase #6	$76.94	3.669%	$79.7629	$79.76	$79.75	$79.80
Purchase #7	$76.26	12.632%	$85.8932	$85.89	$85.90	$85.90
7 purchase totals =	$769.69		$831.8450	$831.85	$831.85	$831.90