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	$73.86	10.454%	$81.5813	$81.58	$81.60	$81.60
Purchase #2	$173.77	7.217%	$186.311	$186.31	$186.30	$186.30
Purchase #3	$49.76	8.625%	$54.0518	$54.05	$54.05	$54.10
Purchase #4	$85.37	6.513%	$90.9301	$90.93	$90.95	$90.90
Purchase #5	$234.32	6.495%	$249.5391	$249.54	$249.55	$249.50
Purchase #6	$39.58	7.465%	$42.5346	$42.53	$42.55	$42.50
Purchase #7	$151.87	13.740%	$172.7369	$172.74	$172.75	$172.70
7 purchase totals =	$808.53		$877.6848	$877.68	$877.75	$877.60