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	$75.35	6.709%	$80.4052	$80.41	$80.40	$80.40
Purchase #2	$136.48	13.755%	$155.2528	$155.25	$155.25	$155.30
Purchase #3	$6.58	12.139%	$7.3787	$7.38	$7.40	$7.40
Purchase #4	$242.26	8.719%	$263.3826	$263.38	$263.40	$263.40
Purchase #5	$72.55	10.503%	$80.1699	$80.17	$80.15	$80.20
Purchase #6	$126.80	10.195%	$139.7273	$139.73	$139.75	$139.70
Purchase #7	$174.46	7.464%	$187.4817	$187.48	$187.50	$187.50
7 purchase totals =	$834.48		$913.7982	$913.80	$913.85	$913.90