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	$50.35	5.607%	$53.1731	$53.17	$53.15	$53.20
Purchase #2	$103.40	6.261%	$109.8739	$109.87	$109.85	$109.90
Purchase #3	$170.79	10.363%	$188.489	$188.49	$188.50	$188.50
Purchase #4	$47.90	10.242%	$52.8059	$52.81	$52.80	$52.80
Purchase #5	$51.73	5.539%	$54.5953	$54.60	$54.60	$54.60
Purchase #6	$189.95	3.301%	$196.2202	$196.22	$196.20	$196.20
Purchase #7	$192.39	5.678%	$203.3139	$203.31	$203.30	$203.30
7 purchase totals =	$806.51		$858.4713	$858.47	$858.40	$858.50