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	$244.86	4.359%	$255.5334	$255.53	$255.55	$255.50
Purchase #2	$35.71	4.275%	$37.2366	$37.24	$37.25	$37.20
Purchase #3	$126.59	12.246%	$142.0922	$142.09	$142.10	$142.10
Purchase #4	$87.54	4.169%	$91.1895	$91.19	$91.20	$91.20
Purchase #5	$71.89	7.141%	$77.0237	$77.02	$77.00	$77.00
Purchase #6	$188.25	8.347%	$203.9632	$203.96	$203.95	$204.00
Purchase #7	$186.27	5.594%	$196.6899	$196.69	$196.70	$196.70
7 purchase totals =	$941.11		$1,003.7285	$1,003.72	$1,003.75	$1,003.70