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	$80.46	11.651%	$89.8344	$89.83	$89.85	$89.80
Purchase #2	$205.29	3.692%	$212.8693	$212.87	$212.85	$212.90
Purchase #3	$56.81	7.400%	$61.0139	$61.01	$61.00	$61.00
Purchase #4	$163.35	7.693%	$175.9165	$175.92	$175.90	$175.90
Purchase #5	$136.53	5.502%	$144.0419	$144.04	$144.05	$144.00
Purchase #6	$21.91	4.423%	$22.8791	$22.88	$22.90	$22.90
Purchase #7	$162.28	7.210%	$173.9804	$173.98	$174.00	$174.00
7 purchase totals =	$826.63		$880.5355	$880.53	$880.55	$880.50