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	$27.61	13.779%	$31.4144	$31.41	$31.40	$31.40
Purchase #2	$168.99	11.743%	$188.8345	$188.83	$188.85	$188.80
Purchase #3	$101.28	4.530%	$105.868	$105.87	$105.85	$105.90
Purchase #4	$56.45	10.476%	$62.3637	$62.36	$62.35	$62.40
Purchase #5	$97.34	6.867%	$104.0243	$104.02	$104.00	$104.00
Purchase #6	$12.27	12.782%	$13.8384	$13.84	$13.85	$13.80
Purchase #7	$152.36	12.631%	$171.6046	$171.60	$171.60	$171.60
7 purchase totals =	$616.30		$677.9479	$677.93	$677.90	$677.90