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	$121.96	13.460%	$138.3758	$138.38	$138.40	$138.40
Purchase #2	$18.62	11.590%	$20.7781	$20.78	$20.80	$20.80
Purchase #3	$45.57	12.448%	$51.2426	$51.24	$51.25	$51.20
Purchase #4	$18.92	8.691%	$20.5643	$20.56	$20.55	$20.60
Purchase #5	$93.96	4.806%	$98.4757	$98.48	$98.50	$98.50
Purchase #6	$95.95	5.710%	$101.4287	$101.43	$101.45	$101.40
Purchase #7	$86.89	5.263%	$91.463	$91.46	$91.45	$91.50
7 purchase totals =	$481.87		$522.3282	$522.33	$522.40	$522.40