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	$101.58	6.713%	$108.3991	$108.40	$108.40	$108.40
Purchase #2	$231.98	5.601%	$244.9732	$244.97	$244.95	$245.00
Purchase #3	$130.50	12.571%	$146.9052	$146.91	$146.90	$146.90
Purchase #4	$162.95	13.543%	$185.0183	$185.02	$185.00	$185.00
Purchase #5	$92.50	8.440%	$100.307	$100.31	$100.30	$100.30
Purchase #6	$176.43	6.755%	$188.3478	$188.35	$188.35	$188.30
Purchase #7	$39.42	10.490%	$43.5552	$43.56	$43.55	$43.60
7 purchase totals =	$935.36		$1,017.5058	$1,017.52	$1,017.45	$1,017.50