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	$185.92	13.569%	$211.1475	$211.15	$211.15	$211.10
Purchase #2	$233.87	9.176%	$255.3299	$255.33	$255.35	$255.30
Purchase #3	$132.63	13.499%	$150.5337	$150.53	$150.55	$150.50
Purchase #4	$199.71	9.124%	$217.9315	$217.93	$217.95	$217.90
Purchase #5	$149.63	12.203%	$167.8893	$167.89	$167.90	$167.90
Purchase #6	$231.80	5.289%	$244.0599	$244.06	$244.05	$244.10
Purchase #7	$90.41	10.319%	$99.7394	$99.74	$99.75	$99.70
7 purchase totals =	$1,223.97		$1,346.6312	$1,346.63	$1,346.70	$1,346.50