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	$89.96	10.624%	$99.5174	$99.52	$99.50	$99.50
Purchase #2	$246.68	6.166%	$261.8903	$261.89	$261.90	$261.90
Purchase #3	$40.61	3.116%	$41.8754	$41.88	$41.90	$41.90
Purchase #4	$222.81	5.469%	$234.9955	$235.00	$235.00	$235.00
Purchase #5	$25.59	10.679%	$28.3228	$28.32	$28.30	$28.30
Purchase #6	$30.92	7.131%	$33.1249	$33.12	$33.10	$33.10
Purchase #7	$163.84	3.113%	$168.9403	$168.94	$168.95	$168.90
7 purchase totals =	$820.41		$868.6666	$868.67	$868.65	$868.60