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	$53.72	9.874%	$59.0243	$59.02	$59.00	$59.00
Purchase #2	$35.72	7.564%	$38.4219	$38.42	$38.40	$38.40
Purchase #3	$224.48	3.787%	$232.9811	$232.98	$233.00	$233.00
Purchase #4	$191.60	6.425%	$203.9103	$203.91	$203.90	$203.90
Purchase #5	$62.29	9.768%	$68.3745	$68.37	$68.35	$68.40
Purchase #6	$127.29	11.756%	$142.2542	$142.25	$142.25	$142.30
Purchase #7	$60.67	7.846%	$65.4302	$65.43	$65.45	$65.40
7 purchase totals =	$755.77		$810.3965	$810.38	$810.35	$810.40