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	$178.48	4.541%	$186.5848	$186.58	$186.60	$186.60
Purchase #2	$29.70	5.449%	$31.3184	$31.32	$31.30	$31.30
Purchase #3	$139.93	4.416%	$146.1093	$146.11	$146.10	$146.10
Purchase #4	$152.87	10.468%	$168.8724	$168.87	$168.85	$168.90
Purchase #5	$222.45	9.812%	$244.2768	$244.28	$244.30	$244.30
Purchase #6	$108.59	5.558%	$114.6254	$114.63	$114.65	$114.60
Purchase #7	$240.98	9.383%	$263.5912	$263.59	$263.60	$263.60
7 purchase totals =	$1,073.00		$1,155.3783	$1,155.38	$1,155.40	$1,155.40