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	$80.97	10.335%	$89.3382	$89.34	$89.35	$89.30
Purchase #2	$100.54	11.725%	$112.3283	$112.33	$112.35	$112.30
Purchase #3	$23.31	10.683%	$25.8002	$25.80	$25.80	$25.80
Purchase #4	$26.77	6.872%	$28.6096	$28.61	$28.60	$28.60
Purchase #5	$192.47	9.139%	$210.0598	$210.06	$210.05	$210.10
Purchase #6	$229.28	6.712%	$244.6693	$244.67	$244.65	$244.70
Purchase #7	$250.49	8.780%	$272.483	$272.48	$272.50	$272.50
7 purchase totals =	$903.83		$983.2884	$983.29	$983.30	$983.30