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	$27.67	12.391%	$31.0986	$31.10	$31.10	$31.10
Purchase #2	$185.51	3.212%	$191.4686	$191.47	$191.45	$191.50
Purchase #3	$156.55	10.581%	$173.1146	$173.11	$173.10	$173.10
Purchase #4	$146.32	3.118%	$150.8823	$150.88	$150.90	$150.90
Purchase #5	$94.45	10.699%	$104.5552	$104.56	$104.55	$104.60
Purchase #6	$246.26	9.162%	$268.8223	$268.82	$268.80	$268.80
Purchase #7	$153.40	10.363%	$169.2968	$169.30	$169.30	$169.30
7 purchase totals =	$1,010.16		$1,089.2384	$1,089.24	$1,089.20	$1,089.30