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	$64.44	10.427%	$71.1592	$71.16	$71.15	$71.20
Purchase #2	$122.56	11.241%	$136.337	$136.34	$136.35	$136.30
Purchase #3	$39.74	6.151%	$42.1844	$42.18	$42.20	$42.20
Purchase #4	$248.83	4.273%	$259.4625	$259.46	$259.45	$259.50
Purchase #5	$35.96	5.572%	$37.9637	$37.96	$37.95	$38.00
Purchase #6	$61.85	7.350%	$66.396	$66.40	$66.40	$66.40
Purchase #7	$90.83	6.731%	$96.9438	$96.94	$96.95	$96.90
7 purchase totals =	$664.21		$710.4466	$710.44	$710.45	$710.50