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	$167.86	6.177%	$178.2287	$178.23	$178.25	$178.20
Purchase #2	$52.68	12.413%	$59.2192	$59.22	$59.20	$59.20
Purchase #3	$169.92	5.715%	$179.6309	$179.63	$179.65	$179.60
Purchase #4	$41.96	3.264%	$43.3296	$43.33	$43.35	$43.30
Purchase #5	$37.68	11.826%	$42.136	$42.14	$42.15	$42.10
Purchase #6	$213.36	12.739%	$240.5399	$240.54	$240.55	$240.50
Purchase #7	$189.87	5.810%	$200.9014	$200.90	$200.90	$200.90
7 purchase totals =	$873.33		$943.9857	$943.99	$944.05	$943.80