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	$123.90	3.356%	$128.0581	$128.06	$128.05	$128.10
Purchase #2	$228.74	3.520%	$236.7916	$236.79	$236.80	$236.80
Purchase #3	$215.33	9.838%	$236.5142	$236.51	$236.50	$236.50
Purchase #4	$62.37	13.863%	$71.0164	$71.02	$71.00	$71.00
Purchase #5	$186.47	7.382%	$200.2352	$200.24	$200.25	$200.20
Purchase #6	$57.52	7.682%	$61.9387	$61.94	$61.95	$61.90
Purchase #7	$209.55	3.369%	$216.6097	$216.61	$216.60	$216.60
7 purchase totals =	$1,083.88		$1,151.1639	$1,151.17	$1,151.15	$1,151.10