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	$85.43	5.374%	$90.021	$90.02	$90.00	$90.00
Purchase #2	$158.58	8.464%	$172.0022	$172.00	$172.00	$172.00
Purchase #3	$218.49	11.787%	$244.2434	$244.24	$244.25	$244.20
Purchase #4	$129.39	7.849%	$139.5458	$139.55	$139.55	$139.50
Purchase #5	$213.71	13.848%	$243.3046	$243.30	$243.30	$243.30
Purchase #6	$142.57	9.654%	$156.3337	$156.33	$156.35	$156.30
Purchase #7	$146.43	12.207%	$164.3047	$164.30	$164.30	$164.30
7 purchase totals =	$1,094.60		$1,209.7554	$1,209.74	$1,209.75	$1,209.60