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	$27.50	8.655%	$29.8801	$29.88	$29.90	$29.90
Purchase #2	$142.88	6.813%	$152.6144	$152.61	$152.60	$152.60
Purchase #3	$213.46	3.805%	$221.5822	$221.58	$221.60	$221.60
Purchase #4	$234.83	8.411%	$254.5816	$254.58	$254.60	$254.60
Purchase #5	$76.77	5.289%	$80.8304	$80.83	$80.85	$80.80
Purchase #6	$42.39	8.374%	$45.9397	$45.94	$45.95	$45.90
Purchase #7	$33.31	11.504%	$37.142	$37.14	$37.15	$37.10
7 purchase totals =	$771.14		$822.5704	$822.56	$822.65	$822.50