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	$246.64	13.646%	$280.2965	$280.30	$280.30	$280.30
Purchase #2	$199.76	4.799%	$209.3465	$209.35	$209.35	$209.30
Purchase #3	$99.66	5.841%	$105.4811	$105.48	$105.50	$105.50
Purchase #4	$127.81	11.708%	$142.774	$142.77	$142.75	$142.80
Purchase #5	$6.31	11.757%	$7.0519	$7.05	$7.05	$7.10
Purchase #6	$200.89	4.484%	$209.8979	$209.90	$209.90	$209.90
Purchase #7	$132.74	4.683%	$138.9562	$138.96	$138.95	$139.00
7 purchase totals =	$1,013.81		$1,093.8041	$1,093.81	$1,093.80	$1,093.90