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	$74.98	5.216%	$78.891	$78.89	$78.90	$78.90
Purchase #2	$166.42	13.496%	$188.88	$188.88	$188.90	$188.90
Purchase #3	$12.44	11.167%	$13.8292	$13.83	$13.85	$13.80
Purchase #4	$126.59	9.719%	$138.8933	$138.89	$138.90	$138.90
Purchase #5	$72.69	12.860%	$82.0379	$82.04	$82.05	$82.00
Purchase #6	$67.52	13.440%	$76.5947	$76.59	$76.60	$76.60
Purchase #7	$216.31	11.331%	$240.8201	$240.82	$240.80	$240.80
7 purchase totals =	$736.95		$819.9462	$819.94	$820.00	$819.90