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	$53.51	3.373%	$55.3149	$55.31	$55.30	$55.30
Purchase #2	$143.85	11.387%	$160.2302	$160.23	$160.25	$160.20
Purchase #3	$37.78	11.773%	$42.2278	$42.23	$42.25	$42.20
Purchase #4	$98.84	11.240%	$109.9496	$109.95	$109.95	$109.90
Purchase #5	$102.56	12.691%	$115.5759	$115.58	$115.60	$115.60
Purchase #6	$204.65	10.328%	$225.7863	$225.79	$225.80	$225.80
Purchase #7	$246.63	4.319%	$257.2819	$257.28	$257.30	$257.30
7 purchase totals =	$887.82		$966.3666	$966.37	$966.45	$966.30