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	$6.96	13.555%	$7.9034	$7.90	$7.90	$7.90
Purchase #2	$59.96	12.612%	$67.5222	$67.52	$67.50	$67.50
Purchase #3	$61.88	9.616%	$67.8304	$67.83	$67.85	$67.80
Purchase #4	$144.51	13.445%	$163.9394	$163.94	$163.95	$163.90
Purchase #5	$152.89	8.381%	$165.7037	$165.70	$165.70	$165.70
Purchase #6	$81.76	4.260%	$85.243	$85.24	$85.25	$85.20
Purchase #7	$189.81	8.393%	$205.7408	$205.74	$205.75	$205.70
7 purchase totals =	$697.77		$763.8829	$763.87	$763.90	$763.70