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	$171.33	5.264%	$180.3488	$180.35	$180.35	$180.30
Purchase #2	$26.72	4.718%	$27.9806	$27.98	$28.00	$28.00
Purchase #3	$94.49	4.504%	$98.7458	$98.75	$98.75	$98.70
Purchase #4	$228.56	12.264%	$256.5906	$256.59	$256.60	$256.60
Purchase #5	$55.82	10.293%	$61.5656	$61.57	$61.55	$61.60
Purchase #6	$113.66	12.120%	$127.4356	$127.44	$127.45	$127.40
Purchase #7	$165.61	5.166%	$174.1654	$174.17	$174.15	$174.20
7 purchase totals =	$856.19		$926.8324	$926.85	$926.85	$926.80