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	$30.40	11.166%	$33.7945	$33.79	$33.80	$33.80
Purchase #2	$166.70	12.803%	$188.0426	$188.04	$188.05	$188.00
Purchase #3	$146.72	11.846%	$164.1005	$164.10	$164.10	$164.10
Purchase #4	$139.82	6.477%	$148.8761	$148.88	$148.90	$148.90
Purchase #5	$39.60	9.167%	$43.2301	$43.23	$43.25	$43.20
Purchase #6	$104.98	4.543%	$109.7492	$109.75	$109.75	$109.70
Purchase #7	$169.86	7.476%	$182.5587	$182.56	$182.55	$182.60
7 purchase totals =	$798.08		$870.3517	$870.35	$870.40	$870.30