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	$225.34	11.257%	$250.7065	$250.71	$250.70	$250.70
Purchase #2	$38.90	6.817%	$41.5518	$41.55	$41.55	$41.60
Purchase #3	$97.85	4.401%	$102.1564	$102.16	$102.15	$102.20
Purchase #4	$30.48	13.711%	$34.6591	$34.66	$34.65	$34.70
Purchase #5	$136.92	3.368%	$141.5315	$141.53	$141.55	$141.50
Purchase #6	$82.28	10.118%	$90.6051	$90.61	$90.60	$90.60
Purchase #7	$63.37	7.185%	$67.9231	$67.92	$67.90	$67.90
7 purchase totals =	$675.14		$729.1335	$729.14	$729.10	$729.20