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	$51.88	5.210%	$54.5829	$54.58	$54.60	$54.60
Purchase #2	$200.54	4.664%	$209.8932	$209.89	$209.90	$209.90
Purchase #3	$21.96	4.250%	$22.8933	$22.89	$22.90	$22.90
Purchase #4	$179.61	4.344%	$187.4123	$187.41	$187.40	$187.40
Purchase #5	$171.50	13.452%	$194.5702	$194.57	$194.55	$194.60
Purchase #6	$239.76	4.659%	$250.9304	$250.93	$250.95	$250.90
Purchase #7	$158.62	6.177%	$168.418	$168.42	$168.40	$168.40
7 purchase totals =	$1,023.87		$1,088.7003	$1,088.69	$1,088.70	$1,088.70