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	$95.94	3.700%	$99.4898	$99.49	$99.50	$99.50
Purchase #2	$64.53	3.125%	$66.5466	$66.55	$66.55	$66.50
Purchase #3	$32.41	3.382%	$33.5061	$33.51	$33.50	$33.50
Purchase #4	$250.31	7.416%	$268.873	$268.87	$268.85	$268.90
Purchase #5	$81.55	10.727%	$90.2979	$90.30	$90.30	$90.30
Purchase #6	$225.45	4.221%	$234.9662	$234.97	$234.95	$235.00
Purchase #7	$114.92	7.263%	$123.2666	$123.27	$123.25	$123.30
7 purchase totals =	$865.11		$916.9462	$916.96	$916.90	$917.00