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	$89.33	11.168%	$99.3064	$99.31	$99.30	$99.30
Purchase #2	$80.25	8.398%	$86.9894	$86.99	$87.00	$87.00
Purchase #3	$80.72	12.438%	$90.76	$90.76	$90.75	$90.80
Purchase #4	$82.88	11.482%	$92.3963	$92.40	$92.40	$92.40
Purchase #5	$173.83	5.182%	$182.8379	$182.84	$182.85	$182.80
Purchase #6	$55.57	7.111%	$59.5216	$59.52	$59.50	$59.50
Purchase #7	$148.80	10.515%	$164.4463	$164.45	$164.45	$164.40
7 purchase totals =	$711.38		$776.2579	$776.27	$776.25	$776.20