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	$30.61	4.222%	$31.9024	$31.90	$31.90	$31.90
Purchase #2	$56.86	10.399%	$62.7729	$62.77	$62.75	$62.80
Purchase #3	$97.36	4.632%	$101.8697	$101.87	$101.85	$101.90
Purchase #4	$69.71	12.315%	$78.2948	$78.29	$78.30	$78.30
Purchase #5	$171.87	3.304%	$177.5486	$177.55	$177.55	$177.50
Purchase #6	$126.72	3.619%	$131.306	$131.31	$131.30	$131.30
Purchase #7	$176.73	8.828%	$192.3317	$192.33	$192.35	$192.30
7 purchase totals =	$729.86		$776.0261	$776.02	$776.00	$776.00