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	$250.89	5.207%	$263.9538	$263.95	$263.95	$264.00
Purchase #2	$64.89	10.249%	$71.5406	$71.54	$71.55	$71.50
Purchase #3	$56.59	5.565%	$59.7392	$59.74	$59.75	$59.70
Purchase #4	$102.39	13.677%	$116.3939	$116.39	$116.40	$116.40
Purchase #5	$60.88	11.709%	$68.0084	$68.01	$68.00	$68.00
Purchase #6	$91.93	9.400%	$100.5714	$100.57	$100.55	$100.60
Purchase #7	$206.53	9.576%	$226.3073	$226.31	$226.30	$226.30
7 purchase totals =	$834.10		$906.5146	$906.51	$906.50	$906.50