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	$44.39	12.148%	$49.7825	$49.78	$49.80	$49.80
Purchase #2	$168.79	10.581%	$186.6497	$186.65	$186.65	$186.60
Purchase #3	$49.30	13.613%	$56.0112	$56.01	$56.00	$56.00
Purchase #4	$145.74	13.473%	$165.3756	$165.38	$165.40	$165.40
Purchase #5	$144.53	4.463%	$150.9804	$150.98	$151.00	$151.00
Purchase #6	$33.71	4.254%	$35.144	$35.14	$35.15	$35.10
Purchase #7	$86.43	10.565%	$95.5613	$95.56	$95.55	$95.60
7 purchase totals =	$672.89		$739.5047	$739.50	$739.55	$739.50