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	$48.48	6.259%	$51.5144	$51.51	$51.50	$51.50
Purchase #2	$245.57	9.468%	$268.8206	$268.82	$268.80	$268.80
Purchase #3	$89.52	3.282%	$92.458	$92.46	$92.45	$92.50
Purchase #4	$75.62	6.293%	$80.3788	$80.38	$80.40	$80.40
Purchase #5	$150.33	9.572%	$164.7196	$164.72	$164.70	$164.70
Purchase #6	$170.69	8.772%	$185.6629	$185.66	$185.65	$185.70
Purchase #7	$57.83	13.834%	$65.8302	$65.83	$65.85	$65.80
7 purchase totals =	$838.04		$909.3845	$909.38	$909.35	$909.40