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	$6.83	8.633%	$7.4196	$7.42	$7.40	$7.40
Purchase #2	$91.79	8.760%	$99.8308	$99.83	$99.85	$99.80
Purchase #3	$172.61	4.121%	$179.7233	$179.72	$179.70	$179.70
Purchase #4	$202.93	5.309%	$213.7036	$213.70	$213.70	$213.70
Purchase #5	$74.43	5.597%	$78.5958	$78.60	$78.60	$78.60
Purchase #6	$64.30	4.327%	$67.0823	$67.08	$67.10	$67.10
Purchase #7	$87.92	12.582%	$98.9821	$98.98	$99.00	$99.00
7 purchase totals =	$700.81		$745.3375	$745.33	$745.35	$745.30