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	$49.96	3.230%	$51.5737	$51.57	$51.55	$51.60
Purchase #2	$75.56	4.250%	$78.7713	$78.77	$78.75	$78.80
Purchase #3	$120.67	12.750%	$136.0554	$136.06	$136.05	$136.10
Purchase #4	$201.27	11.605%	$224.6274	$224.63	$224.65	$224.60
Purchase #5	$71.47	9.781%	$78.4605	$78.46	$78.45	$78.50
Purchase #6	$64.80	8.580%	$70.3598	$70.36	$70.35	$70.40
Purchase #7	$62.86	7.132%	$67.3432	$67.34	$67.35	$67.30
7 purchase totals =	$646.59		$707.1913	$707.19	$707.15	$707.30