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	$102.92	6.171%	$109.2712	$109.27	$109.25	$109.30
Purchase #2	$229.74	8.472%	$249.2036	$249.20	$249.20	$249.20
Purchase #3	$241.95	5.456%	$255.1508	$255.15	$255.15	$255.20
Purchase #4	$51.48	11.652%	$57.4784	$57.48	$57.50	$57.50
Purchase #5	$113.31	5.127%	$119.1194	$119.12	$119.10	$119.10
Purchase #6	$36.88	9.655%	$40.4408	$40.44	$40.45	$40.40
Purchase #7	$51.28	8.190%	$55.4798	$55.48	$55.50	$55.50
7 purchase totals =	$827.56		$886.1440	$886.14	$886.15	$886.20