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	$20.95	6.557%	$22.3237	$22.32	$22.30	$22.30
Purchase #2	$195.79	13.655%	$222.5251	$222.53	$222.55	$222.50
Purchase #3	$201.33	4.116%	$209.6167	$209.62	$209.60	$209.60
Purchase #4	$48.50	7.144%	$51.9648	$51.96	$51.95	$52.00
Purchase #5	$93.26	10.604%	$103.1493	$103.15	$103.15	$103.10
Purchase #6	$30.90	6.349%	$32.8618	$32.86	$32.85	$32.90
Purchase #7	$116.60	12.501%	$131.1762	$131.18	$131.20	$131.20
7 purchase totals =	$707.33		$773.6176	$773.62	$773.60	$773.60