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	$55.73	7.211%	$59.7487	$59.75	$59.75	$59.70
Purchase #2	$210.80	12.685%	$237.54	$237.54	$237.55	$237.50
Purchase #3	$76.69	8.130%	$82.9249	$82.92	$82.90	$82.90
Purchase #4	$72.49	10.442%	$80.0594	$80.06	$80.05	$80.10
Purchase #5	$104.91	6.597%	$111.8309	$111.83	$111.85	$111.80
Purchase #6	$178.93	13.435%	$202.9692	$202.97	$202.95	$203.00
Purchase #7	$63.33	11.321%	$70.4996	$70.50	$70.50	$70.50
7 purchase totals =	$762.88		$845.5727	$845.57	$845.55	$845.50