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	$139.46	12.560%	$156.9762	$156.98	$157.00	$157.00
Purchase #2	$109.54	12.379%	$123.1	$123.10	$123.10	$123.10
Purchase #3	$74.71	8.279%	$80.8952	$80.90	$80.90	$80.90
Purchase #4	$248.82	9.359%	$272.1071	$272.11	$272.10	$272.10
Purchase #5	$224.83	3.872%	$233.5354	$233.54	$233.55	$233.50
Purchase #6	$67.89	10.207%	$74.8195	$74.82	$74.80	$74.80
Purchase #7	$127.85	11.475%	$142.5208	$142.52	$142.50	$142.50
7 purchase totals =	$993.10		$1,083.9542	$1,083.97	$1,083.95	$1,083.90