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	$126.41	5.675%	$133.5838	$133.58	$133.60	$133.60
Purchase #2	$80.28	12.320%	$90.1705	$90.17	$90.15	$90.20
Purchase #3	$176.62	7.280%	$189.4779	$189.48	$189.50	$189.50
Purchase #4	$143.82	12.718%	$162.111	$162.11	$162.10	$162.10
Purchase #5	$182.86	7.372%	$196.3404	$196.34	$196.35	$196.30
Purchase #6	$243.68	6.483%	$259.4778	$259.48	$259.50	$259.50
Purchase #7	$237.27	7.205%	$254.3653	$254.37	$254.35	$254.40
7 purchase totals =	$1,190.94		$1,285.5267	$1,285.53	$1,285.55	$1,285.60