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	$24.92	3.166%	$25.709	$25.71	$25.70	$25.70
Purchase #2	$7.88	10.755%	$8.7275	$8.73	$8.75	$8.70
Purchase #3	$133.67	12.529%	$150.4175	$150.42	$150.40	$150.40
Purchase #4	$116.89	9.772%	$128.3125	$128.31	$128.30	$128.30
Purchase #5	$29.97	11.760%	$33.4945	$33.49	$33.50	$33.50
Purchase #6	$106.89	4.625%	$111.8337	$111.83	$111.85	$111.80
Purchase #7	$235.63	6.278%	$250.4229	$250.42	$250.40	$250.40
7 purchase totals =	$655.85		$708.9176	$708.91	$708.90	$708.80