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	$28.89	11.652%	$32.2563	$32.26	$32.25	$32.30
Purchase #2	$18.76	12.230%	$21.0543	$21.05	$21.05	$21.10
Purchase #3	$59.88	8.844%	$65.1758	$65.18	$65.20	$65.20
Purchase #4	$41.90	3.861%	$43.5178	$43.52	$43.50	$43.50
Purchase #5	$74.94	6.777%	$80.0187	$80.02	$80.00	$80.00
Purchase #6	$226.73	13.193%	$256.6425	$256.64	$256.65	$256.60
Purchase #7	$92.68	6.281%	$98.5012	$98.50	$98.50	$98.50
7 purchase totals =	$543.78		$597.1666	$597.17	$597.15	$597.20