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	$105.36	6.700%	$112.4191	$112.42	$112.40	$112.40
Purchase #2	$33.67	13.411%	$38.1855	$38.19	$38.20	$38.20
Purchase #3	$171.57	9.263%	$187.4625	$187.46	$187.45	$187.50
Purchase #4	$96.59	6.348%	$102.7215	$102.72	$102.70	$102.70
Purchase #5	$199.63	11.416%	$222.4198	$222.42	$222.40	$222.40
Purchase #6	$157.73	9.165%	$172.186	$172.19	$172.20	$172.20
Purchase #7	$41.28	4.655%	$43.2016	$43.20	$43.20	$43.20
7 purchase totals =	$805.83		$878.5960	$878.60	$878.55	$878.60