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	$242.76	3.721%	$251.7931	$251.79	$251.80	$251.80
Purchase #2	$51.89	8.845%	$56.4797	$56.48	$56.50	$56.50
Purchase #3	$179.67	5.667%	$189.8519	$189.85	$189.85	$189.90
Purchase #4	$188.25	12.484%	$211.7511	$211.75	$211.75	$211.80
Purchase #5	$10.54	13.518%	$11.9648	$11.96	$11.95	$12.00
Purchase #6	$47.80	11.721%	$53.4026	$53.40	$53.40	$53.40
Purchase #7	$80.89	12.165%	$90.7303	$90.73	$90.75	$90.70
7 purchase totals =	$801.80		$865.9735	$865.96	$866.00	$866.10