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	$178.47	4.577%	$186.6386	$186.64	$186.65	$186.60
Purchase #2	$60.69	11.432%	$67.6281	$67.63	$67.65	$67.60
Purchase #3	$71.88	8.200%	$77.7742	$77.77	$77.75	$77.80
Purchase #4	$23.57	8.439%	$25.5591	$25.56	$25.55	$25.60
Purchase #5	$89.83	6.440%	$95.6151	$95.62	$95.60	$95.60
Purchase #6	$57.81	3.611%	$59.8975	$59.90	$59.90	$59.90
Purchase #7	$62.83	7.651%	$67.6371	$67.64	$67.65	$67.60
7 purchase totals =	$545.08		$580.7497	$580.76	$580.75	$580.70