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	$67.92	3.428%	$70.2483	$70.25	$70.25	$70.20
Purchase #2	$90.44	11.103%	$100.4816	$100.48	$100.50	$100.50
Purchase #3	$86.93	6.241%	$92.3553	$92.36	$92.35	$92.40
Purchase #4	$80.27	4.504%	$83.8854	$83.89	$83.90	$83.90
Purchase #5	$12.67	5.670%	$13.3884	$13.39	$13.40	$13.40
Purchase #6	$23.79	5.146%	$25.0142	$25.01	$25.00	$25.00
Purchase #7	$141.63	11.759%	$158.2843	$158.28	$158.30	$158.30
7 purchase totals =	$503.65		$543.6575	$543.66	$543.70	$543.70