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	$90.67	10.683%	$100.3563	$100.36	$100.35	$100.40
Purchase #2	$223.67	12.155%	$250.8571	$250.86	$250.85	$250.90
Purchase #3	$247.26	13.116%	$279.6906	$279.69	$279.70	$279.70
Purchase #4	$246.93	8.408%	$267.6919	$267.69	$267.70	$267.70
Purchase #5	$196.98	3.279%	$203.439	$203.44	$203.45	$203.40
Purchase #6	$124.40	5.326%	$131.0255	$131.03	$131.05	$131.00
Purchase #7	$116.92	9.211%	$127.6895	$127.69	$127.70	$127.70
7 purchase totals =	$1,246.83		$1,360.7499	$1,360.76	$1,360.80	$1,360.80