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	$61.29	10.622%	$67.8002	$67.80	$67.80	$67.80
Purchase #2	$139.59	10.801%	$154.6671	$154.67	$154.65	$154.70
Purchase #3	$25.42	8.543%	$27.5916	$27.59	$27.60	$27.60
Purchase #4	$77.67	9.741%	$85.2358	$85.24	$85.25	$85.20
Purchase #5	$7.86	9.164%	$8.5803	$8.58	$8.60	$8.60
Purchase #6	$48.63	12.846%	$54.877	$54.88	$54.90	$54.90
Purchase #7	$123.66	13.679%	$140.5755	$140.58	$140.60	$140.60
7 purchase totals =	$484.12		$539.3275	$539.34	$539.40	$539.40