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	$237.97	3.840%	$247.108	$247.11	$247.10	$247.10
Purchase #2	$42.60	12.524%	$47.9352	$47.94	$47.95	$47.90
Purchase #3	$28.59	3.617%	$29.6241	$29.62	$29.60	$29.60
Purchase #4	$221.82	3.415%	$229.3952	$229.40	$229.40	$229.40
Purchase #5	$83.66	7.479%	$89.9169	$89.92	$89.90	$89.90
Purchase #6	$95.32	3.376%	$98.538	$98.54	$98.55	$98.50
Purchase #7	$82.87	7.236%	$88.8665	$88.87	$88.85	$88.90
7 purchase totals =	$792.83		$831.3839	$831.40	$831.35	$831.30