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	$218.85	13.840%	$249.1388	$249.14	$249.15	$249.10
Purchase #2	$233.73	5.479%	$246.5361	$246.54	$246.55	$246.50
Purchase #3	$114.55	11.480%	$127.7003	$127.70	$127.70	$127.70
Purchase #4	$52.70	13.595%	$59.8646	$59.86	$59.85	$59.90
Purchase #5	$224.66	4.401%	$234.5473	$234.55	$234.55	$234.50
Purchase #6	$91.75	12.333%	$103.0655	$103.07	$103.05	$103.10
Purchase #7	$156.84	7.728%	$168.9606	$168.96	$168.95	$169.00
7 purchase totals =	$1,093.08		$1,189.8132	$1,189.82	$1,189.80	$1,189.80