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	$179.59	11.517%	$200.2734	$200.27	$200.25	$200.30
Purchase #2	$110.60	6.486%	$117.7735	$117.77	$117.75	$117.80
Purchase #3	$140.63	8.705%	$152.8718	$152.87	$152.85	$152.90
Purchase #4	$119.67	9.720%	$131.3019	$131.30	$131.30	$131.30
Purchase #5	$82.56	9.649%	$90.5262	$90.53	$90.55	$90.50
Purchase #6	$212.35	3.462%	$219.7016	$219.70	$219.70	$219.70
Purchase #7	$80.47	4.435%	$84.0388	$84.04	$84.05	$84.00
7 purchase totals =	$925.87		$996.4872	$996.48	$996.45	$996.50