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	$150.66	11.872%	$168.5464	$168.55	$168.55	$168.50
Purchase #2	$19.39	13.154%	$21.9406	$21.94	$21.95	$21.90
Purchase #3	$79.39	12.680%	$89.4567	$89.46	$89.45	$89.50
Purchase #4	$123.89	6.487%	$131.9267	$131.93	$131.95	$131.90
Purchase #5	$6.88	5.497%	$7.2582	$7.26	$7.25	$7.30
Purchase #6	$141.97	8.850%	$154.5343	$154.53	$154.55	$154.50
Purchase #7	$213.84	10.575%	$236.4536	$236.45	$236.45	$236.50
7 purchase totals =	$736.02		$810.1165	$810.12	$810.15	$810.10