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	$121.67	6.263%	$129.2902	$129.29	$129.30	$129.30
Purchase #2	$59.73	11.856%	$66.8116	$66.81	$66.80	$66.80
Purchase #3	$241.63	10.722%	$267.5376	$267.54	$267.55	$267.50
Purchase #4	$124.57	5.654%	$131.6132	$131.61	$131.60	$131.60
Purchase #5	$73.89	8.385%	$80.0857	$80.09	$80.10	$80.10
Purchase #6	$128.82	9.761%	$141.3941	$141.39	$141.40	$141.40
Purchase #7	$163.67	9.666%	$179.4903	$179.49	$179.50	$179.50
7 purchase totals =	$913.98		$996.2227	$996.22	$996.25	$996.20