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	$235.37	8.570%	$255.5412	$255.54	$255.55	$255.50
Purchase #2	$101.74	6.574%	$108.4284	$108.43	$108.45	$108.40
Purchase #3	$170.51	7.164%	$182.7253	$182.73	$182.75	$182.70
Purchase #4	$72.91	6.167%	$77.4064	$77.41	$77.40	$77.40
Purchase #5	$179.44	12.244%	$201.4106	$201.41	$201.40	$201.40
Purchase #6	$133.33	13.196%	$150.9242	$150.92	$150.90	$150.90
Purchase #7	$51.94	6.105%	$55.1109	$55.11	$55.10	$55.10
7 purchase totals =	$945.24		$1,031.5470	$1,031.55	$1,031.55	$1,031.40