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	$59.64	4.794%	$62.4991	$62.50	$62.50	$62.50
Purchase #2	$38.35	3.166%	$39.5642	$39.56	$39.55	$39.60
Purchase #3	$188.66	11.597%	$210.5389	$210.54	$210.55	$210.50
Purchase #4	$94.31	11.424%	$105.084	$105.08	$105.10	$105.10
Purchase #5	$6.29	12.789%	$7.0944	$7.09	$7.10	$7.10
Purchase #6	$74.56	3.430%	$77.1174	$77.12	$77.10	$77.10
Purchase #7	$36.61	9.129%	$39.9521	$39.95	$39.95	$40.00
7 purchase totals =	$498.42		$541.8501	$541.84	$541.85	$541.90