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	$77.57	4.434%	$81.0095	$81.01	$81.00	$81.00
Purchase #2	$31.50	7.682%	$33.9198	$33.92	$33.90	$33.90
Purchase #3	$57.94	6.292%	$61.5856	$61.59	$61.60	$61.60
Purchase #4	$178.73	4.672%	$187.0803	$187.08	$187.10	$187.10
Purchase #5	$44.59	10.242%	$49.1569	$49.16	$49.15	$49.20
Purchase #6	$64.59	11.649%	$72.1141	$72.11	$72.10	$72.10
Purchase #7	$135.83	4.744%	$142.2738	$142.27	$142.25	$142.30
7 purchase totals =	$590.75		$627.1400	$627.14	$627.10	$627.20