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	$159.26	13.223%	$180.3189	$180.32	$180.30	$180.30
Purchase #2	$153.56	3.756%	$159.3277	$159.33	$159.35	$159.30
Purchase #3	$109.58	6.320%	$116.5055	$116.51	$116.50	$116.50
Purchase #4	$187.40	3.661%	$194.2607	$194.26	$194.25	$194.30
Purchase #5	$137.38	7.538%	$147.7357	$147.74	$147.75	$147.70
Purchase #6	$85.99	10.103%	$94.6776	$94.68	$94.70	$94.70
Purchase #7	$82.48	4.121%	$85.879	$85.88	$85.90	$85.90
7 purchase totals =	$915.65		$978.7051	$978.72	$978.75	$978.70