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	$129.57	10.764%	$143.5169	$143.52	$143.50	$143.50
Purchase #2	$156.72	6.190%	$166.421	$166.42	$166.40	$166.40
Purchase #3	$223.88	4.196%	$233.274	$233.27	$233.25	$233.30
Purchase #4	$124.53	10.484%	$137.5857	$137.59	$137.60	$137.60
Purchase #5	$24.33	7.298%	$26.1056	$26.11	$26.10	$26.10
Purchase #6	$164.98	10.574%	$182.425	$182.43	$182.45	$182.40
Purchase #7	$63.59	13.577%	$72.2236	$72.22	$72.20	$72.20
7 purchase totals =	$887.60		$961.5518	$961.56	$961.50	$961.50