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	$237.27	5.637%	$250.6449	$250.64	$250.65	$250.60
Purchase #2	$166.63	12.190%	$186.9422	$186.94	$186.95	$186.90
Purchase #3	$137.81	9.535%	$150.9502	$150.95	$150.95	$151.00
Purchase #4	$131.97	5.300%	$138.9644	$138.96	$138.95	$139.00
Purchase #5	$144.38	6.638%	$153.9639	$153.96	$153.95	$154.00
Purchase #6	$95.98	5.102%	$100.8769	$100.88	$100.90	$100.90
Purchase #7	$101.33	7.831%	$109.2652	$109.27	$109.25	$109.30
7 purchase totals =	$1,015.37		$1,091.6077	$1,091.60	$1,091.60	$1,091.70