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	$33.72	5.269%	$35.4967	$35.50	$35.50	$35.50
Purchase #2	$63.97	12.729%	$72.1127	$72.11	$72.10	$72.10
Purchase #3	$244.29	7.466%	$262.5287	$262.53	$262.55	$262.50
Purchase #4	$160.53	4.254%	$167.3589	$167.36	$167.35	$167.40
Purchase #5	$118.58	10.318%	$130.8151	$130.82	$130.80	$130.80
Purchase #6	$144.83	12.502%	$162.9366	$162.94	$162.95	$162.90
Purchase #7	$24.55	10.430%	$27.1106	$27.11	$27.10	$27.10
7 purchase totals =	$790.47		$858.3593	$858.37	$858.35	$858.30