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	$198.75	5.765%	$210.2079	$210.21	$210.20	$210.20
Purchase #2	$24.65	11.350%	$27.4478	$27.45	$27.45	$27.40
Purchase #3	$98.39	4.147%	$102.4702	$102.47	$102.45	$102.50
Purchase #4	$29.76	12.432%	$33.4598	$33.46	$33.45	$33.50
Purchase #5	$99.40	12.345%	$111.6709	$111.67	$111.65	$111.70
Purchase #6	$234.33	9.503%	$256.5984	$256.60	$256.60	$256.60
Purchase #7	$73.63	5.581%	$77.7393	$77.74	$77.75	$77.70
7 purchase totals =	$758.91		$819.5943	$819.60	$819.55	$819.60