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	$25.79	10.361%	$28.4621	$28.46	$28.45	$28.50
Purchase #2	$178.31	12.319%	$200.276	$200.28	$200.30	$200.30
Purchase #3	$59.44	7.314%	$63.7874	$63.79	$63.80	$63.80
Purchase #4	$183.59	12.371%	$206.3019	$206.30	$206.30	$206.30
Purchase #5	$117.72	5.797%	$124.5442	$124.54	$124.55	$124.50
Purchase #6	$40.48	12.657%	$45.6036	$45.60	$45.60	$45.60
Purchase #7	$133.41	9.161%	$145.6317	$145.63	$145.65	$145.60
7 purchase totals =	$738.74		$814.6069	$814.60	$814.65	$814.60