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	$144.77	4.709%	$151.5872	$151.59	$151.60	$151.60
Purchase #2	$117.93	11.802%	$131.8481	$131.85	$131.85	$131.80
Purchase #3	$31.54	4.502%	$32.9599	$32.96	$32.95	$33.00
Purchase #4	$81.45	10.400%	$89.9208	$89.92	$89.90	$89.90
Purchase #5	$159.96	9.703%	$175.4809	$175.48	$175.50	$175.50
Purchase #6	$75.77	5.507%	$79.9427	$79.94	$79.95	$79.90
Purchase #7	$220.49	4.184%	$229.7153	$229.72	$229.70	$229.70
7 purchase totals =	$831.91		$891.4549	$891.46	$891.45	$891.40