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	$26.89	11.690%	$30.0334	$30.03	$30.05	$30.00
Purchase #2	$67.93	7.216%	$72.8318	$72.83	$72.85	$72.80
Purchase #3	$45.49	5.535%	$48.0079	$48.01	$48.00	$48.00
Purchase #4	$61.45	7.469%	$66.0397	$66.04	$66.05	$66.00
Purchase #5	$213.56	12.600%	$240.4686	$240.47	$240.45	$240.50
Purchase #6	$70.96	10.433%	$78.3633	$78.36	$78.35	$78.40
Purchase #7	$136.78	8.187%	$147.9782	$147.98	$148.00	$148.00
7 purchase totals =	$623.06		$683.7229	$683.72	$683.75	$683.70