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	$175.32	9.239%	$191.5178	$191.52	$191.50	$191.50
Purchase #2	$52.71	6.264%	$56.0118	$56.01	$56.00	$56.00
Purchase #3	$31.83	13.231%	$36.0414	$36.04	$36.05	$36.00
Purchase #4	$210.57	13.270%	$238.5126	$238.51	$238.50	$238.50
Purchase #5	$45.77	9.650%	$50.1868	$50.19	$50.20	$50.20
Purchase #6	$67.70	6.451%	$72.0673	$72.07	$72.05	$72.10
Purchase #7	$29.37	12.311%	$32.9857	$32.99	$33.00	$33.00
7 purchase totals =	$613.27		$677.3234	$677.33	$677.30	$677.30