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	$121.73	4.786%	$127.556	$127.56	$127.55	$127.60
Purchase #2	$131.57	7.844%	$141.8904	$141.89	$141.90	$141.90
Purchase #3	$51.33	11.228%	$57.0933	$57.09	$57.10	$57.10
Purchase #4	$33.60	12.504%	$37.8013	$37.80	$37.80	$37.80
Purchase #5	$50.38	12.145%	$56.4987	$56.50	$56.50	$56.50
Purchase #6	$184.72	12.693%	$208.1665	$208.17	$208.15	$208.20
Purchase #7	$27.97	6.591%	$29.8135	$29.81	$29.80	$29.80
7 purchase totals =	$601.30		$658.8197	$658.82	$658.80	$658.90