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	$245.99	11.209%	$273.563	$273.56	$273.55	$273.60
Purchase #2	$37.29	11.248%	$41.4844	$41.48	$41.50	$41.50
Purchase #3	$131.80	10.334%	$145.4202	$145.42	$145.40	$145.40
Purchase #4	$219.66	10.496%	$242.7155	$242.72	$242.70	$242.70
Purchase #5	$66.82	13.705%	$75.9777	$75.98	$76.00	$76.00
Purchase #6	$12.62	9.182%	$13.7788	$13.78	$13.80	$13.80
Purchase #7	$55.81	7.114%	$59.7803	$59.78	$59.80	$59.80
7 purchase totals =	$769.99		$852.7199	$852.72	$852.75	$852.80