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	$115.91	7.380%	$124.4642	$124.46	$124.45	$124.50
Purchase #2	$18.93	12.418%	$21.2807	$21.28	$21.30	$21.30
Purchase #3	$215.47	10.480%	$238.0513	$238.05	$238.05	$238.10
Purchase #4	$84.51	9.386%	$92.4421	$92.44	$92.45	$92.40
Purchase #5	$154.78	6.472%	$164.7974	$164.80	$164.80	$164.80
Purchase #6	$82.29	8.326%	$89.1415	$89.14	$89.15	$89.10
Purchase #7	$29.29	7.678%	$31.5389	$31.54	$31.55	$31.50
7 purchase totals =	$701.18		$761.7161	$761.71	$761.75	$761.70