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	$55.87	5.404%	$58.8892	$58.89	$58.90	$58.90
Purchase #2	$51.96	10.351%	$57.3384	$57.34	$57.35	$57.30
Purchase #3	$232.78	7.233%	$249.617	$249.62	$249.60	$249.60
Purchase #4	$232.46	3.155%	$239.7941	$239.79	$239.80	$239.80
Purchase #5	$193.46	10.497%	$213.7675	$213.77	$213.75	$213.80
Purchase #6	$175.41	9.789%	$192.5809	$192.58	$192.60	$192.60
Purchase #7	$99.52	12.384%	$111.8446	$111.84	$111.85	$111.80
7 purchase totals =	$1,041.46		$1,123.8317	$1,123.83	$1,123.85	$1,123.80