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	$52.77	11.383%	$58.7768	$58.78	$58.80	$58.80
Purchase #2	$117.43	11.572%	$131.019	$131.02	$131.00	$131.00
Purchase #3	$76.29	3.121%	$78.671	$78.67	$78.65	$78.70
Purchase #4	$135.66	4.688%	$142.0197	$142.02	$142.00	$142.00
Purchase #5	$185.50	7.858%	$200.0766	$200.08	$200.10	$200.10
Purchase #6	$37.74	4.607%	$39.4787	$39.48	$39.50	$39.50
Purchase #7	$37.45	6.340%	$39.8243	$39.82	$39.80	$39.80
7 purchase totals =	$642.84		$689.8661	$689.87	$689.85	$689.90