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	$235.82	10.841%	$261.3852	$261.39	$261.40	$261.40
Purchase #2	$98.58	6.430%	$104.9187	$104.92	$104.90	$104.90
Purchase #3	$127.31	13.536%	$144.5427	$144.54	$144.55	$144.50
Purchase #4	$79.76	4.256%	$83.1546	$83.15	$83.15	$83.20
Purchase #5	$96.54	13.795%	$109.8577	$109.86	$109.85	$109.90
Purchase #6	$13.96	13.656%	$15.8664	$15.87	$15.85	$15.90
Purchase #7	$174.41	4.567%	$182.3753	$182.38	$182.40	$182.40
7 purchase totals =	$826.38		$902.1006	$902.11	$902.10	$902.20