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	$10.35	3.577%	$10.7202	$10.72	$10.70	$10.70
Purchase #2	$152.54	10.507%	$168.5674	$168.57	$168.55	$168.60
Purchase #3	$120.96	7.570%	$130.1167	$130.12	$130.10	$130.10
Purchase #4	$11.93	11.413%	$13.2916	$13.29	$13.30	$13.30
Purchase #5	$37.53	3.853%	$38.976	$38.98	$39.00	$39.00
Purchase #6	$59.45	12.337%	$66.7843	$66.78	$66.80	$66.80
Purchase #7	$79.95	10.440%	$88.2968	$88.30	$88.30	$88.30
7 purchase totals =	$472.71		$516.7530	$516.76	$516.75	$516.80