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	$168.88	9.326%	$184.6297	$184.63	$184.65	$184.60
Purchase #2	$159.73	4.445%	$166.83	$166.83	$166.85	$166.80
Purchase #3	$36.95	10.456%	$40.8135	$40.81	$40.80	$40.80
Purchase #4	$174.71	8.702%	$189.9133	$189.91	$189.90	$189.90
Purchase #5	$108.56	13.737%	$123.4729	$123.47	$123.45	$123.50
Purchase #6	$157.49	10.709%	$174.3556	$174.36	$174.35	$174.40
Purchase #7	$73.41	10.256%	$80.9389	$80.94	$80.95	$80.90
7 purchase totals =	$879.73		$960.9539	$960.95	$960.95	$960.90