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	$103.77	5.526%	$109.5043	$109.50	$109.50	$109.50
Purchase #2	$237.28	9.254%	$259.2379	$259.24	$259.25	$259.20
Purchase #3	$141.49	13.648%	$160.8006	$160.80	$160.80	$160.80
Purchase #4	$74.90	9.753%	$82.205	$82.21	$82.20	$82.20
Purchase #5	$214.46	8.776%	$233.281	$233.28	$233.30	$233.30
Purchase #6	$159.76	4.774%	$167.3869	$167.39	$167.40	$167.40
Purchase #7	$78.43	10.215%	$86.4416	$86.44	$86.45	$86.40
7 purchase totals =	$1,010.09		$1,098.8573	$1,098.86	$1,098.90	$1,098.80