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	$71.50	9.604%	$78.3669	$78.37	$78.35	$78.40
Purchase #2	$162.47	12.461%	$182.7154	$182.72	$182.70	$182.70
Purchase #3	$136.95	4.624%	$143.2826	$143.28	$143.30	$143.30
Purchase #4	$249.62	13.326%	$282.8844	$282.88	$282.90	$282.90
Purchase #5	$235.58	13.599%	$267.6165	$267.62	$267.60	$267.60
Purchase #6	$64.68	11.783%	$72.3012	$72.30	$72.30	$72.30
Purchase #7	$60.34	7.141%	$64.6489	$64.65	$64.65	$64.60
7 purchase totals =	$981.14		$1,091.8159	$1,091.82	$1,091.80	$1,091.80