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	$36.70	12.553%	$41.307	$41.31	$41.30	$41.30
Purchase #2	$171.99	8.110%	$185.9384	$185.94	$185.95	$185.90
Purchase #3	$113.71	13.376%	$128.9198	$128.92	$128.90	$128.90
Purchase #4	$173.63	6.695%	$185.2545	$185.25	$185.25	$185.30
Purchase #5	$155.54	8.347%	$168.5229	$168.52	$168.50	$168.50
Purchase #6	$36.44	10.133%	$40.1325	$40.13	$40.15	$40.10
Purchase #7	$131.91	13.175%	$149.2891	$149.29	$149.30	$149.30
7 purchase totals =	$819.92		$899.3642	$899.36	$899.35	$899.30