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	$63.81	12.313%	$71.6669	$71.67	$71.65	$71.70
Purchase #2	$39.51	7.791%	$42.5882	$42.59	$42.60	$42.60
Purchase #3	$116.52	5.819%	$123.3003	$123.30	$123.30	$123.30
Purchase #4	$55.89	6.280%	$59.3999	$59.40	$59.40	$59.40
Purchase #5	$176.72	7.836%	$190.5678	$190.57	$190.55	$190.60
Purchase #6	$22.98	11.199%	$25.5535	$25.55	$25.55	$25.60
Purchase #7	$58.59	11.668%	$65.4263	$65.43	$65.45	$65.40
7 purchase totals =	$534.02		$578.5029	$578.51	$578.50	$578.60