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	$84.81	6.854%	$90.6229	$90.62	$90.60	$90.60
Purchase #2	$110.51	4.872%	$115.894	$115.89	$115.90	$115.90
Purchase #3	$158.87	8.429%	$172.2612	$172.26	$172.25	$172.30
Purchase #4	$210.80	11.270%	$234.5572	$234.56	$234.55	$234.60
Purchase #5	$71.90	8.545%	$78.0439	$78.04	$78.05	$78.00
Purchase #6	$43.61	5.284%	$45.9144	$45.91	$45.90	$45.90
Purchase #7	$161.79	8.576%	$175.6651	$175.67	$175.65	$175.70
7 purchase totals =	$842.29		$912.9587	$912.95	$912.90	$913.00