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	$157.44	7.481%	$169.2181	$169.22	$169.20	$169.20
Purchase #2	$38.56	5.854%	$40.8173	$40.82	$40.80	$40.80
Purchase #3	$148.86	11.686%	$166.2558	$166.26	$166.25	$166.30
Purchase #4	$229.77	9.124%	$250.7342	$250.73	$250.75	$250.70
Purchase #5	$133.37	13.383%	$151.2189	$151.22	$151.20	$151.20
Purchase #6	$215.37	9.697%	$236.2544	$236.25	$236.25	$236.30
Purchase #7	$68.71	6.205%	$72.9735	$72.97	$72.95	$73.00
7 purchase totals =	$992.08		$1,087.4722	$1,087.47	$1,087.40	$1,087.50