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	$85.37	7.188%	$91.5064	$91.51	$91.50	$91.50
Purchase #2	$141.25	10.668%	$156.3186	$156.32	$156.30	$156.30
Purchase #3	$94.41	13.743%	$107.3848	$107.38	$107.40	$107.40
Purchase #4	$196.99	8.706%	$214.1399	$214.14	$214.15	$214.10
Purchase #5	$59.34	8.538%	$64.4064	$64.41	$64.40	$64.40
Purchase #6	$150.65	9.438%	$164.8683	$164.87	$164.85	$164.90
Purchase #7	$95.39	4.141%	$99.3401	$99.34	$99.35	$99.30
7 purchase totals =	$823.40		$897.9645	$897.97	$897.95	$897.90