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	$163.33	13.383%	$185.1885	$185.19	$185.20	$185.20
Purchase #2	$123.73	11.117%	$137.4851	$137.49	$137.50	$137.50
Purchase #3	$141.59	9.837%	$155.5182	$155.52	$155.50	$155.50
Purchase #4	$59.59	13.392%	$67.5703	$67.57	$67.55	$67.60
Purchase #5	$234.68	5.261%	$247.0265	$247.03	$247.05	$247.00
Purchase #6	$6.62	11.604%	$7.3882	$7.39	$7.40	$7.40
Purchase #7	$110.55	11.383%	$123.1339	$123.13	$123.15	$123.10
7 purchase totals =	$840.09		$923.3107	$923.32	$923.35	$923.30