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	$75.82	6.285%	$80.5853	$80.59	$80.60	$80.60
Purchase #2	$135.98	4.827%	$142.5438	$142.54	$142.55	$142.50
Purchase #3	$6.30	13.135%	$7.1275	$7.13	$7.15	$7.10
Purchase #4	$82.55	11.276%	$91.8583	$91.86	$91.85	$91.90
Purchase #5	$204.28	5.529%	$215.5746	$215.57	$215.55	$215.60
Purchase #6	$49.41	11.465%	$55.0749	$55.07	$55.05	$55.10
Purchase #7	$48.58	11.459%	$54.1468	$54.15	$54.15	$54.10
7 purchase totals =	$602.92		$646.9112	$646.91	$646.90	$646.90