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	$166.58	13.196%	$188.5619	$188.56	$188.55	$188.60
Purchase #2	$150.83	12.665%	$169.9326	$169.93	$169.95	$169.90
Purchase #3	$100.96	4.561%	$105.5648	$105.56	$105.55	$105.60
Purchase #4	$153.85	9.755%	$168.8581	$168.86	$168.85	$168.90
Purchase #5	$6.69	12.532%	$7.5284	$7.53	$7.55	$7.50
Purchase #6	$105.46	9.569%	$115.5515	$115.55	$115.55	$115.60
Purchase #7	$72.71	5.512%	$76.7178	$76.72	$76.70	$76.70
7 purchase totals =	$757.08		$832.7151	$832.71	$832.70	$832.80