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	$248.96	10.722%	$275.6535	$275.65	$275.65	$275.70
Purchase #2	$29.99	3.748%	$31.114	$31.11	$31.10	$31.10
Purchase #3	$99.40	13.597%	$112.9154	$112.92	$112.90	$112.90
Purchase #4	$168.37	6.824%	$179.8596	$179.86	$179.85	$179.90
Purchase #5	$65.44	11.128%	$72.7222	$72.72	$72.70	$72.70
Purchase #6	$94.92	9.449%	$103.889	$103.89	$103.90	$103.90
Purchase #7	$6.73	9.413%	$7.3635	$7.36	$7.35	$7.40
7 purchase totals =	$713.81		$783.5172	$783.51	$783.45	$783.60