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	$101.76	11.402%	$113.3627	$113.36	$113.35	$113.40
Purchase #2	$219.79	4.771%	$230.2762	$230.28	$230.30	$230.30
Purchase #3	$83.87	4.523%	$87.6634	$87.66	$87.65	$87.70
Purchase #4	$104.57	6.181%	$111.0335	$111.03	$111.05	$111.00
Purchase #5	$79.46	3.611%	$82.3293	$82.33	$82.35	$82.30
Purchase #6	$38.36	10.600%	$42.4262	$42.43	$42.45	$42.40
Purchase #7	$228.35	11.521%	$254.6582	$254.66	$254.65	$254.70
7 purchase totals =	$856.16		$921.7495	$921.75	$921.80	$921.80