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	$82.46	11.448%	$91.9	$91.90	$91.90	$91.90
Purchase #2	$132.96	11.801%	$148.6506	$148.65	$148.65	$148.70
Purchase #3	$86.81	4.424%	$90.6505	$90.65	$90.65	$90.70
Purchase #4	$131.35	9.588%	$143.9438	$143.94	$143.95	$143.90
Purchase #5	$184.39	10.654%	$204.0349	$204.03	$204.05	$204.00
Purchase #6	$81.32	5.400%	$85.7113	$85.71	$85.70	$85.70
Purchase #7	$134.85	11.237%	$150.0031	$150.00	$150.00	$150.00
7 purchase totals =	$834.14		$914.8942	$914.88	$914.90	$914.90