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	$154.84	13.273%	$175.3919	$175.39	$175.40	$175.40
Purchase #2	$112.30	6.761%	$119.8926	$119.89	$119.90	$119.90
Purchase #3	$189.27	3.814%	$196.4888	$196.49	$196.50	$196.50
Purchase #4	$152.55	4.217%	$158.983	$158.98	$159.00	$159.00
Purchase #5	$128.43	11.488%	$143.184	$143.18	$143.20	$143.20
Purchase #6	$250.91	9.775%	$275.4365	$275.44	$275.45	$275.40
Purchase #7	$55.40	10.495%	$61.2142	$61.21	$61.20	$61.20
7 purchase totals =	$1,043.70		$1,130.5910	$1,130.58	$1,130.65	$1,130.60