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	$246.63	11.336%	$274.588	$274.59	$274.60	$274.60
Purchase #2	$235.46	6.268%	$250.2186	$250.22	$250.20	$250.20
Purchase #3	$152.92	6.326%	$162.5937	$162.59	$162.60	$162.60
Purchase #4	$128.66	7.136%	$137.8412	$137.84	$137.85	$137.80
Purchase #5	$20.82	7.668%	$22.4165	$22.42	$22.40	$22.40
Purchase #6	$218.77	13.326%	$247.9233	$247.92	$247.90	$247.90
Purchase #7	$43.47	9.111%	$47.4306	$47.43	$47.45	$47.40
7 purchase totals =	$1,046.73		$1,143.0119	$1,143.01	$1,143.00	$1,142.90